Complete blood count

Source: Wikipedia, the free encyclopedia.
(Redirected from
White blood cell count
)

Complete blood count
See caption
A CBC specimen in front of a printout displaying CBC and differential results
SynonymsComplete blood cell count,[1] full blood count (FBC),[2] full blood cell count,[3] full blood examination (FBE),[2] hemogram[4]
MeSHD001772
MedlinePlus003642
LOINCCodes for CBC, e.g., 57021-8
HCPCS-L2G0306

A complete blood count (CBC), also known as a full blood count (FBC), is a set of

platelets, the concentration of hemoglobin, and the hematocrit (the volume percentage of red blood cells). The red blood cell indices, which indicate the average size and hemoglobin content of red blood cells, are also reported, and a white blood cell differential
, which counts the different types of white blood cells, may be included.

The CBC is often carried out as part of a medical assessment and can be used to monitor health or diagnose diseases. The results are interpreted by comparing them to

. Not all results falling outside of the reference range require medical intervention.

The CBC is usually performed by an automated hematology analyzer, which counts cells and collects information on their size and structure. The concentration of hemoglobin is measured, and the red blood cell indices are calculated from measurements of red blood cells and hemoglobin. Manual tests can be used to independently confirm abnormal results. Approximately 10–25% of samples require a manual blood smear review,[5] in which the blood is stained and viewed under a microscope to verify that the analyzer results are consistent with the appearance of the cells and to look for abnormalities. The hematocrit can be determined manually by centrifuging the sample and measuring the proportion of red blood cells, and in laboratories without access to automated instruments, blood cells are counted under the microscope using a hemocytometer.

In 1852,

Coulter principle, which was patented by Wallace H. Coulter in 1953. The Coulter principle uses electrical impedance measurements to count blood cells and determine their sizes; it is a technology that remains in use in many automated analyzers. Further research in the 1970s involved the use of optical
measurements to count and identify cells, which enabled the automation of the white blood cell differential.

Purpose

white blood cells are part of the immune system. The platelets are needed to form clots
, which prevent excessive bleeding.

Blood is composed of a fluid portion, called

platelets.[note 1][7] The complete blood count evaluates the three cellular components of blood. Some medical conditions, such as anemia or thrombocytopenia, are defined by marked increases or decreases in blood cell counts.[8] Changes in many organ systems may affect the blood, so CBC results are useful for investigating a wide range of conditions. Because of the amount of information it provides, the complete blood count is one of the most commonly performed medical laboratory tests.[9][10][11]

The CBC is often used to

bleeding disorder, or some cancers. People who have been diagnosed with disorders that may cause abnormal CBC results or who are receiving treatments that can affect blood cell counts may have a regular CBC performed to monitor their health,[4][12] and the test is often performed each day on people who are hospitalized.[13] The results may indicate a need for a blood or platelet transfusion.[14]

The complete blood count has specific applications in many

newborn babies, a CBC may be needed to investigate jaundice or to count the number of immature cells in the white blood cell differential, which can be an indicator of sepsis.[27][28]

The complete blood count is an essential tool of

The

hospital-acquired anemia and may result in unnecessary transfusions.[38]

Procedure

CBC performed by the fingerstick method, using an Abbott Cell-Dyn 1700 automated analyzer

The sample is collected by drawing blood into a tube containing an

heelprick in babies.[42][43] Testing is typically performed on an automated analyzer, but manual techniques such as a blood smear examination or manual hematocrit test can be used to investigate abnormal results.[44] Cell counts and hemoglobin measurements are performed manually in laboratories lacking access to automated instruments.[45]

Automated

On board the analyzer, the sample is agitated to evenly distribute the cells, then diluted and partitioned into at least two channels, one of which is used to count red blood cells and platelets, the other to count white blood cells and determine the hemoglobin concentration. Some instruments measure hemoglobin in a separate channel, and additional channels may be used for differential white blood cell counts, reticulocyte counts and specialized measurements of platelets.[46][47][48] The cells are suspended in a fluid stream and their properties are measured as they flow past sensors in a technique known as flow cytometry.[note 3][49][52] Hydrodynamic focusing may be used to isolate individual cells so that more accurate results can be obtained: the diluted sample is injected into a stream of low-pressure fluid, which causes the cells in the sample to line up in single file through laminar flow.[53][54]

Sysmex XT-4000i automated hematology analyzer
Schematic of the Coulter principle. A particle suspended in a conductive medium passes through an aperture, causing an increase in impedance
The Coulter principle—the transient current drop is proportional to the particle volume

To measure the hemoglobin concentration, a

nanometres—corresponds with the concentration of hemoglobin.[56][57]

Sensors count and identify the cells in the sample using two main principles:

electrical conductivity. The amplitude of the voltage pulse generated as a cell crosses the aperture correlates with the amount of fluid displaced by the cell, and thus the cell's volume,[59][60] while the total number of pulses correlates with the number of cells in the sample. The distribution of cell volumes is plotted on a histogram, and by setting volume thresholds based on the typical sizes of each type of cell, the different cell populations can be identified and counted.[61]

In light scattering techniques, light from a

tungsten-halogen lamp is directed at the stream of cells to collect information about their size and structure. Cells scatter light at different angles as they pass through the beam, which is detected using photometers.[62] Forward scatter, which refers to the amount of light scattered along the beam's axis, is mainly caused by diffraction of light and correlates with cellular size, while side scatter (light scattered at a 90-degree angle) is caused by reflection and refraction and provides information about cellular complexity.[62][63]

fluorescent staining, multi-angle light scatter and monoclonal antibody tagging.[48]

Most analyzers directly measure the average size of red blood cells, which is called the

mean cell volume (MCV), and calculate the hematocrit by multiplying the red blood cell count by the MCV. Some measure the hematocrit by comparing the total volume of red blood cells to the volume of blood sampled, and derive the MCV from the hematocrit and red blood cell count.[66] The hemoglobin concentration, the red blood cell count and the hematocrit are used to calculate the average amount of hemoglobin within each red blood cell, the mean corpuscular hemoglobin (MCH); and its concentration, the mean corpuscular hemoglobin concentration (MCHC).[67] Another calculation, the red blood cell distribution width (RDW), is derived from the standard deviation of the mean cell volume and reflects variation in cellular size.[68]

A scatter plot displaying many differently coloured clusters, labelled with the type of white blood cell they correspond to.
Example of a white blood cell differential scattergram: differently coloured clusters indicate different cell populations

After being treated with reagents, white blood cells form three distinct peaks when their volumes are plotted on a histogram. These peaks correspond roughly to populations of

photomicrographs of the blood smear. The cell images are displayed to a human operator, who can manually re-classify the cells if necessary.[75]

Most analyzers take less than a minute to run all the tests in the complete blood count.[58] Because analyzers sample and count many individual cells, the results are very precise.[76] However, some abnormal cells may not be identified correctly, requiring manual review of the instrument's results and identification by other means of abnormal cells the instrument could not categorize.[5][77]

Point-of-care testing

i-STAT, which derives a hemoglobin reading by estimating the concentration of red blood cells from the conductivity of the blood.[79] Hemoglobin and hematocrit can be measured on point-of-care devices designed for blood gas testing, but these measurements sometimes correlate poorly with those obtained through standard methods.[78] There are simplified versions of hematology analyzers designed for use in clinics that can provide a complete blood count and differential.[80]

Manual

Diagram of the manual hematocrit test showing the fraction of red blood cells measured as 0.46.
Manual determination of hematocrit. The blood has been centrifuged, separating it into red blood cells and plasma.

The tests can be performed manually when automated equipment is not available or when the analyzer results indicate that further investigation is needed.

paraprotein disorders like multiple myeloma, high levels of protein in the blood may cause red blood cells to appear stacked together on the smear, which is termed rouleaux.[85] Some parasitic diseases, such as malaria and babesiosis, can be detected by finding the causative organisms on the blood smear,[86] and the platelet count can be estimated from the blood smear, which is useful if the automated platelet count is inaccurate.[77]

To perform a manual white blood cell differential, the microscopist counts 100 cells on the blood smear and classifies them based on their appearance; sometimes 200 cells are counted.

blast cells seen in acute leukemia.[89] Clinically significant features like toxic granulation and vacuolation can also be ascertained from microscopic examination of white blood cells.[90]

The hematocrit can performed manually by filling a capillary tube with blood, centrifuging it, and measuring the percentage of the blood that consists of red blood cells.[66] This is useful in some conditions that can cause automated hematocrit results to be incorrect, such as polycythemia (a highly elevated red blood cell count)[66] or severe leukocytosis (a highly elevated white blood cell count, which interferes with red blood cell measurements by causing white blood cells to be counted as red cells).[91]

=A glass slide containing two chambers to hold fluid, topped with a coverslip
A microscopic image showing numerous cells overlaid on a grid
Left: A modified Fuchs-Rosenthal hemocytometer. Right: View through the microscope of the hemocytometer. The built-in grid helps to keep track of which cells have been counted.

Red and white blood cells and platelets can be counted using a

light microscope, can make platelets easier to identify.[94] The manual red blood cell count is rarely performed, as it is inaccurate and other methods such as hemoglobinometry and the manual hematocrit are available for assessing red blood cells; but if it is necessary to do so, red blood cells can be counted in blood that has been diluted with saline.[95]

Hemoglobin can be measured manually using a

spectrophotometer or colorimeter. To measure hemoglobin manually, the sample is diluted using reagents that destroy red blood cells to release the hemoglobin. Other chemicals are used to convert different types of hemoglobin to one form, allowing it to be easily measured. The solution is then placed in a measuring cuvette and the absorbance is measured at a specific wavelength, which depends on the type of reagent used. A reference standard containing a known amount of hemoglobin is used to determine the relationship between the absorbance and the hemoglobin concentration, allowing the hemoglobin level of the sample to be measured.[96]

In rural and economically disadvantaged areas, available testing is limited by access to equipment and personnel. At primary care facilities in these regions, testing may be limited to examination of red cell morphology and manual measurement of hemoglobin, while more complex techniques like manual cell counts and differentials, and sometimes automated cell counts, are performed at district laboratories. Regional and provincial hospitals and academic centres typically have access to automated analyzers. Where laboratory facilities are not available, an estimate of hemoglobin concentration can be obtained by placing a drop of blood on a standardized type of absorbent paper and comparing it to a colour scale.[97]

Quality control

Automated analyzers have to be regularly

calibrated. Most manufacturers provide preserved blood with defined parameters and the analyzers are adjusted if the results are outside defined thresholds.[98] To ensure that results continue to be accurate, quality control samples, which are typically provided by the instrument manufacturer, are tested at least once per day. The samples are formulated to provide specific results, and laboratories compare their results against the known values to ensure the instrument is functioning properly.[99][100] For laboratories without access to commercial quality control material, an Indian regulatory organization recommends running patient samples in duplicate and comparing the results.[101] A moving average measurement, in which the average results for patient samples are measured at set intervals, can be used as an additional quality control technique. Assuming that the characteristics of the patient population remain roughly the same over time, the average should remain constant; large shifts in the average value can indicate instrument problems.[99][100] The MCHC values are particularly useful in this regard.[102]

In addition to analyzing internal quality control samples with known results, laboratories may receive external quality assessment samples from regulatory organizations. While the purpose of internal quality control is to ensure that analyzer results are reproducible within a given laboratory, external quality assessment verifies that results from different laboratories are consistent with each other and with the target values.[103] The expected results for external quality assessment samples are not disclosed to the laboratory.[104] External quality assessment programs have been widely adopted in North America and western Europe,[99] and laboratories are often required to participate in these programs to maintain accreditation.[105] Logistical issues may make it difficult for laboratories in under-resourced areas to implement external quality assessment schemes.[106]

Included tests

The CBC measures the amounts of platelets and red and white blood cells, along with the hemoglobin and hematocrit values. Red blood cell indices—MCV, MCH and MCHC—which describe the size of red blood cells and their hemoglobin content, are reported along with the red blood cell distribution width (RDW), which measures the amount of variation in the sizes of red blood cells. A white blood cell differential, which enumerates the different types of white blood cells, may be performed, and a count of immature red blood cells (reticulocytes) is sometimes included.[4][107]

Red blood cells, hemoglobin, and hematocrit

Sample CBC in microcytic anemia
Analyte Result Normal range
Red cell count 5.5 x 1012/L 4.5–5.7
White cell count 9.8 x 109/L 4.0–10.0
Hemoglobin 123 g/L 133–167
Hematocrit 0.42 0.35–0.53
MCV 76 fL 77–98
MCH 22.4 pg 26–33
MCHC 293 g/L 330–370
RDW 14.5% 10.3–15.3
An example of CBC results showing a low hemoglobin, MCV, MCH and MCHC. The person was anemic. The cause could be iron deficiency or a hemoglobinopathy.[108]

Red blood cells deliver

femtolitres or cubic micrometres.[4] By multiplying the mean cell volume by the red blood cell count, the hematocrit (HCT) or packed cell volume (PCV), a measurement of the percentage of blood that is made up of red blood cells, can be derived;[66] and when the hematocrit is performed directly, the mean cell volume may be calculated from the hematocrit and red blood cell count.[110][111] Hemoglobin, measured after the red blood cells are lysed, is usually reported in units of grams per litre (g/L) or grams per decilitre (g/dL).[112] Assuming that the red blood cells are normal, there is a constant relationship between hemoglobin and hematocrit: the hematocrit percentage is approximately three times greater than the hemoglobin value in g/dL, plus or minus three. This relationship, called the rule of three, can be used to confirm that CBC results are correct.[113]

Two other measurements are calculated from the red blood cell count, the hemoglobin concentration, and the hematocrit: the mean corpuscular hemoglobin and the mean corpuscular hemoglobin concentration.[114][115] These parameters describe the hemoglobin content of each red blood cell. The MCH and MCHC can be confusing; in essence the MCH is a measure of the average amount of hemoglobin per red blood cell. The MCHC gives the average proportion of the cell that is hemoglobin. The MCH does not take into account the size of the red blood cells whereas the MCHC does.[116] Collectively, the MCV, MCH, and MCHC are referred to as the red blood cell indices.[114][115] Changes in these indices are visible on the blood smear: red blood cells that are abnormally large or small can be identified by comparison to the sizes of white blood cells, and cells with a low hemoglobin concentration appear pale.[117] Another parameter is calculated from the initial measurements of red blood cells: the red blood cell distribution width or RDW, which reflects the degree of variation in the cells' size.[118]

hypochromia), and vary greatly in size (anisocytosis
).

An abnormally low hemoglobin, hematocrit, or red blood cell count indicates anemia.

erythropoeisis), decreased production of red blood cells (insufficient erythropoeisis), and increased destruction of red blood cells (hemolytic anemia).[120] Anemia reduces the blood's ability to carry oxygen, causing symptoms like tiredness and shortness of breath.[121] If the hemoglobin level falls below thresholds based on the person's clinical condition, a blood transfusion may be necessary.[122]

An increased number of red blood cells, leading to an increase in the hemoglobin and hematocrit,

heart disease, or when a person has abnormally high levels of erythropoietin, a hormone that stimulates production of red blood cells. In polycythemia vera, the bone marrow produces red cells and other blood cells at an excessively high rate.[127]

Evaluation of red blood cell indices is helpful in determining the cause of anemia. If the MCV is low, the anemia is termed

lipids in the blood (which causes a false increase in the hemoglobin result).[128][131]

Microcytic anemia is typically associated with iron deficiency, thalassemia, and

B12 deficiency, use of some drugs, and some bone marrow diseases. Acute blood loss, hemolytic anemia, bone marrow disorders, and various chronic diseases can result in anemia with a normocytic blood picture.[115][132] The MCV serves an additional purpose in laboratory quality control. It is relatively stable over time compared to other CBC parameters, so a large change in MCV may indicate that the sample was drawn from the wrong patient.[133]

A low RDW has no clinical significance, but an elevated RDW represents increased variation in red blood cell size, a condition known as

iron deficiency anemia and anemia due to vitamin B12 or folate deficiency, while people with thalassemia may have a normal RDW.[118] Based on the CBC results, further steps can be taken to investigate anemia, such as a ferritin test to confirm the presence of iron deficiency, or hemoglobin electrophoresis to diagnose a hemoglobinopathy such as thalassemia or sickle cell disease.[134]

White blood cells

Sample CBC in chronic myeloid leukemia
Analyte Result
White cell count 98.8 x 109/L
Hemoglobin 116 g/L
Hematocrit 0.349 L/L
MCV 89.0 fL
Platelet count 1070 x 109/L
Analyte Result
Neutrophils 48%
Lymphocytes 3%
Monocytes 4%
Eosinophils 3%
Basophils 21%
Band neutrophils 8%
Metamyelocytes 3%
Myelocytes 8%
Blast cells 2%
The white blood cell and platelet counts are markedly increased, and anemia is present. The differential count shows
blast cells.[135]

White blood cells defend against infections and are involved in the

myeloproliferative and lymphoproliferative disorders.[137] A decreased white blood cell count, termed leukopenia, can lead to an increased risk of acquiring infections,[138] and occurs in treatments like chemotherapy and radiation therapy and many conditions that inhibit the production of blood cells.[139] Sepsis is associated with both leukocytosis and leukopenia.[140] The total white blood cell count is usually reported in cells per microlitre of blood (/μL) or 109 cells per litre (× 109/L).[4]

In the white blood cell differential, the different types of white blood cells are identified and counted. The results are reported as a percentage and as an absolute number per unit volume. Five types of white blood cells—

promyelocytes, myelocytes and metamyelocytes.[note 5][144] Other cell types are reported if they are identified in the manual differential.[145]

Differential results are useful in diagnosing and monitoring many medical conditions. For example, an elevated neutrophil count (

congenital disorders and may occur transiently after viral or bacterial infections in children.[150] People with severe neutropenia and clinical signs of infection are treated with antibiotics to prevent potentially life-threatening disease.[151]

chronic myeloid leukemia
: many immature and abnormal white blood cells are visible.

An increased number of

Platelets

See caption.
Blood film of essential thrombocythemia. Platelets are visible as small purple structures.

Platelets play an essential role in clotting. When the wall of a

Thrombocytosis, meaning a high platelet count, may occur in states of inflammation or trauma,[163] as well as in iron deficiency,[164] and the platelet count may reach exceptionally high levels in people with essential thrombocythemia, a rare blood disease.[163] The platelet count can be reported in units of cells per microlitre of blood (/μL),[165] 103 cells per microlitre (× 103/μL), or 109 cells per litre (× 109/L).[4]

The mean platelet volume (MPV) measures the average size of platelets in femtolitres. It can aid in determining the cause of thrombocytopenia; an elevated MPV may occur when young platelets are released into the bloodstream to compensate for increased destruction of platelets, while decreased production of platelets due to dysfunction of the bone marrow can result in a low MPV. The MPV is also useful for differentiating between congenital diseases that cause thrombocytopenia.[118][166] The immature platelet fraction (IPF) or reticulated platelet count is reported by some analyzers and provides information about the rate of platelet production by measuring the number of immature platelets in the blood.[167]

Other tests

Reticulocyte count

Microscopic image of red blood cells stained blue.
Red blood cells stained with new methylene blue: the cells containing dark blue structures are reticulocytes.

Reticulocytes are immature red blood cells, which, unlike the mature cells, contain RNA. A reticulocyte count is sometimes performed as part of a complete blood count, usually to investigate the cause of a person's anemia or evaluate their response to treatment. Anemia with a high reticulocyte count can indicate that the bone marrow is producing red blood cells at a higher rate to compensate for blood loss or hemolysis,[74] while anemia with a low reticulocyte count may suggest that the person has a condition that reduces the body's ability to produce red blood cells.[168] When people with nutritional anemia are given nutrient supplementation, an increase in the reticulocyte count indicates that their body is responding to the treatment by producing more red blood cells.[169] Hematology analyzers perform reticulocyte counts by staining red blood cells with a dye that binds to RNA and measuring the number of reticulocytes through light scattering or fluorescence analysis. The test can be performed manually by staining the blood with new methylene blue and counting the percentage of red blood cells containing RNA under the microscope. The reticulocyte count is expressed as an absolute number[168] or as a percentage of red blood cells.[170]

Some instruments measure the average amount of hemoglobin in each reticulocyte; a parameter that has been studied as an indicator of iron deficiency in people who have conditions that interfere with standard tests.

bone marrow transplantation.[172]

Nucleated red blood cells

See caption.
Blood smear from a newborn baby, showing a few nucleated red cells

During their formation in bone marrow, and in the liver and spleen in fetuses,[173] red blood cells contain a cell nucleus, which is usually absent in the mature cells that circulate in the bloodstream. Nucleated red blood cells are normal in newborn babies,[174] but when detected in children and adults, they indicate an increased demand for red blood cells, which can be caused by bleeding, some cancers and anemia.[118] Most analyzers can detect these cells as part of the differential cell count. High numbers of nucleated red cells can cause a falsely high white cell count, which will require adjusting.[175]

Other parameters

Advanced hematology analyzers generate novel measurements of blood cells which have shown diagnostic significance in research studies but have not yet found widespread clinical use.

coordinate readings indicating the size and position of each white blood cell cluster. These parameters (termed cell population data)[176] have been studied as potential markers for blood disorders, bacterial infections and malaria. Analyzers that use myeloperoxidase staining to produce differential counts can measure white blood cells' expression of the enzyme, which is altered in various disorders.[75] Some instruments can report the percentage of red blood cells that are hypochromic in addition to reporting the average MCHC value, or provide a count of fragmented red cells (schistocytes),[171] which occur in some types of hemolytic anemia.[177] Because these parameters are often specific to particular brands of analyzers, it is difficult for laboratories to interpret and compare results.[171]

Reference ranges

Example of reference ranges for complete blood count with differential (CBC w DIFF)[178]
Test Units Adult Pediatric

(4–7 years old)

Neonate

(0–1 days old)

WBC × 109/L 3.6–10.6 5.0–17.0 9.0–37.0
RBC × 1012/L
  • M: 4.20–6.00
  • F: 3.80–5.20
4.00–5.20 4.10–6.10
HGB g/L
  • M: 135–180
  • F: 120–150
102–152 165–215
HCT L/L
  • M: 0.40–0.54
  • F: 0.35–0.49
0.36–0.46 0.48–0.68
MCV fL 80–100 78–94 95–125
MCH pg 26–34 23–31 30–42
MCHC g/L 320–360 320–360 300–340
RDW % 11.5–14.5 11.5–14.5 elevated[note 6]
PLT × 109/L 150–450 150–450 150–450
Neutrophils × 109/L 1.7–7.5 1.5–11.0 3.7–30.0
Lymphocytes × 109/L 1.0–3.2 1.5–11.1 1.6–14.1
Monocytes × 109/L 0.1–1.3 0.1–1.9 0.1–4.4
Eosinophils × 109/L 0.0–0.3 0.0–0.7 0.0–1.5
Basophils × 109/L 0.0–0.2 0.0–0.3 0.0–0.7

The complete blood count is interpreted by comparing the output to reference ranges, which represent the results found in 95% of apparently healthy people.[35] Based on a statistical normal distribution, the tested samples' ranges vary with sex and age.[179]

On average, adult females have lower hemoglobin, hematocrit, and red blood cell count values than males; the difference lessens, but is still present, after menopause.[180] CBC results for children and newborn babies differ from those of adults. Newborns' hemoglobin, hematocrit, and red blood cell count are extremely high to compensate for low oxygen levels in the womb and the high proportion of fetal hemoglobin, which is less effective at delivering oxygen to tissues than mature forms of hemoglobin, inside their red blood cells.[181][182] The MCV is also increased, and the white blood cell count is elevated with a preponderance of neutrophils.[181][183] The red blood cell count and related values begin to decline shortly after birth, reaching their lowest point at about two months of age and increasing thereafter.[184][185] The red blood cells of older infants and children are smaller, with a lower MCH, than those of adults. In the pediatric white blood cell differential, lymphocytes often outnumber neutrophils, while in adults neutrophils predominate.[181]

Other differences between populations may affect the reference ranges: for example, people living at higher altitudes have higher hemoglobin, hematocrit, and RBC results, and people of African heritage have lower white blood cell counts on average.[186] The type of analyzer used to run the CBC affects the reference ranges as well. Reference ranges are therefore established by individual laboratories based on their own patient populations and equipment.[187][188]

Limitations

Some medical conditions or problems with the blood sample may produce inaccurate results. If the sample is visibly clotted, which can be caused by poor phlebotomy technique, it is unsuitable for testing, because the platelet count will be falsely decreased and other results may be abnormal.[189][190] Samples stored at room temperature for several hours may give falsely high readings for MCV (mean corpuscular volume),[191] because red blood cells swell as they absorb water from the plasma; and platelet and white blood cell differential results may be inaccurate in aged specimens, as the cells degrade over time.[91]

Red blood cell agglutination
: clumps of red blood cells are visible on the blood smear

Samples drawn from individuals with very high levels of bilirubin or lipids in their plasma (referred to as an icteric sample or a lipemic sample, respectively)[192] may show falsely high readings for hemoglobin, because these substances change the colour and opacity of the sample, which interferes with hemoglobin measurement.[193] This effect can be mitigated by replacing the plasma with saline.[91]

Some individuals produce an antibody that causes their platelets to form clumps when their blood is drawn into tubes containing EDTA, the anticoagulant typically used to collect CBC samples. Platelet clumps may be counted as single platelets by automated analyzers, leading to a falsely decreased platelet count. This can be avoided by using an alternative anticoagulant such as sodium citrate or heparin.[194][195]

Another antibody-mediated condition that can affect complete blood count results is

warm autoimmune hemolytic anemia may exhibit red cell agglutination that does not resolve on warming.[130]

While blast and lymphoma cells can be identified in the manual differential, microscopic examination cannot reliably determine the cells'

markers that provide additional information about the cells.[197][198]

History

A black leather case with its contents: a candle and colour cards
An early hemoglobinometer: blood samples were compared to a colour chart of reference standards to determine the hemoglobin level.[199]

Before

Proceedings of the Royal Society of London.[202] Jan Swammerdam had described red blood cells some years earlier, but did not publish his findings at the time. Throughout the 18th and 19th centuries, improvements in microscope technology such as achromatic lenses allowed white blood cells and platelets to be counted in unstained samples.[203]

The physiologist

Karl Vierordt is credited with performing the first blood count.[8][204][205] His technique, published in 1852, involved aspirating a carefully measured volume of blood into a capillary tube and spreading it onto a microscope slide coated with egg white. After the blood dried, he counted every cell on the slide; this process could take more than three hours to complete.[206] The hemocytometer, introduced in 1874 by Louis-Charles Malassez, simplified the microscopic counting of blood cells.[207] Malassez's hemocytometer consisted of a microscope slide containing a flattened capillary tube. Diluted blood was introduced to the capillary chamber by means of a rubber tube attached to one end, and an eyepiece with a scaled grid was attached to the microscope, permitting the microscopist to count the number of cells per volume of blood. In 1877, William Gowers invented a hemocytometer with a built-in counting grid, eliminating the need to produce specially calibrated eyepieces for each microscope.[208]

Black and white portrait of Dmitri Leonidovich Romanowsky
Dmitri Leonidovich Romanowsky invented Romanowsky staining.

In the 1870s, Paul Ehrlich developed a staining technique using a combination of an acidic and basic dye that could distinguish different types of white blood cells and allow red blood cell morphology to be examined.[203] Dmitri Leonidovich Romanowsky improved on this technique in the 1890s, using a mixture of eosin and aged methylene blue to produce a wide range of hues not present when either of the stains was used alone. This became the basis for Romanowsky staining, the technique still used to stain blood smears for manual review.[209]

The first techniques for measuring hemoglobin were devised in the late 19th century, and involved visual comparisons of the colour of diluted blood against a known standard.[205] Attempts to automate this process using spectrophotometry and colorimetry were limited by the fact that hemoglobin is present in the blood in many different forms, meaning that it could not be measured at a single wavelength. In 1920, a method to convert the different forms of hemoglobin to one stable form (cyanmethemoglobin or hemiglobincyanide) was introduced, allowing hemoglobin levels to be measured automatically. The cyanmethemoglobin method remains the reference method for hemoglobin measurement and is still used in many automated hematology analyzers.[57][210][211]

University of Tulane to determine normal ranges for red blood cell parameters, and invented a method known as the Wintrobe hematocrit. Hematocrit measurements had previously been described in the literature, but Wintrobe's method differed in that it used a large tube that could be mass-produced to precise specifications, with a built-in scale. The fraction of red blood cells in the tube was measured after centrifugation to determine the hematocrit. The invention of a reproducible method for determining hematocrit values allowed Wintrobe to define the red blood cell indices.[205]

A complex tube and flask apparatus attached to a measurement station
Model A Coulter counter

Research into automated cell counting began in the early 20th century.

bombing of Hiroshima and Nagasaki,[213] attempted to improve on photoelectric cell counting techniques.[note 7] His research was aided by his brother, Joseph R. Coulter, in a basement laboratory in Chicago.[60] Their results using photoelectric methods were disappointing, and in 1948, after reading a paper relating the conductivity of blood to its red blood cell concentration, Wallace devised the Coulter principle—the theory that a cell suspended in a conductive medium generates a drop in current proportional to its size as it passes through an aperture.[213]

That October, Wallace built a counter to demonstrate the principle. Owing to financial constraints, the aperture was made by burning a hole through a piece of cellophane from a cigarette package.

manometer to provide precise control over sample size, the brothers founded Coulter Electronics Inc. in 1958 to market their instruments. The Coulter counter was initially designed for counting red blood cells, but with later modifications it proved effective for counting white blood cells.[60] Coulter counters were widely adopted by medical laboratories.[211]

The first analyzer able to produce multiple cell counts simultaneously was the

Technicon SMA 4A−7A, released in 1965. It achieved this by partitioning blood samples into two channels: one for counting red and white blood cells and one for measuring hemoglobin. However, the instrument was unreliable and difficult to maintain. In 1968, the Coulter Model S analyzer was released and gained widespread use. Similarly to the Technicon instrument, it used two different reaction chambers, one of which was used for the red cell count, and one of which was used for the white blood cell count and hemoglobin determination. The Model S also determined the mean cell volume using impedance measurements, which allowed the red blood cell indices and hematocrit to be derived. Automated platelet counts were introduced in 1970 with Technicon's Hemalog-8 instrument and were adopted by Coulter's S Plus series analyzers in 1980.[214]

After basic cell counting had been automated, the white blood cell differential remained a challenge. Throughout the 1970s, researchers explored two methods for automating the differential count: digital image processing and flow cytometry. Using technology developed in the 1950s and 60s to automate the reading of

Early flow cytometry devices shot beams of light at cells in specific wavelengths and measured the resulting absorbance, fluorescence or light scatter, collecting information about the cells' features and allowing cellular contents such as

Explanatory notes

  1. ^ Though commonly referred to as such, platelets are technically not cells: they are cell fragments, formed from the cytoplasm of megakaryocytes in the bone marrow.[6]
  2. ^ The data used to construct reference ranges is usually derived from "normal" subjects, but it is possible for these individuals to have asymptomatic disease.[34]
  3. ^ In its broadest sense, the term flow cytometry refers to any measurement of the properties of individual cells in a fluid stream,[49][50] and in this respect, all hematology analyzers (except those using digital image processing) are flow cytometers. However, the term is commonly used in reference to light scattering and fluorescence methods, especially those involving the identification of cells using labelled antibodies that bind to cell surface markers (immunophenotyping).[49][51]
  4. ^ This is not always the case. In some types of thalassemia, for example, a high red blood cell count occurs alongside a low or normal hemoglobin, as the red blood cells are very small.[123][124] The Mentzer index, which compares the MCV to the RBC count, can be used to distinguish between iron deficiency anemia and thalassemia.[125]
  5. ^ Automated instruments group these three types of cells together under the "immature granulocyte" classification,[142] but they are counted separately in the manual differential.[143]
  6. ^ The RDW is highly elevated at birth and gradually decreases until approximately six months of age.[178]
  7. US Navy ships; other accounts claim it was originally designed during the Second World War to count plankton. However, Wallace never worked for the Navy, and his earliest writings on the device state that it was first used to analyze blood. The paint story was eventually retracted from documents produced by the Wallace H. Coulter Foundation.[213]

References

Citations

  1. .
  2. ^ a b HealthDirect (August 2018). "Full blood count". HealthDirect.gov.au. Archived from the original on 2 April 2019. Retrieved 8 September 2020.
  3. ^ "Blood tests: Chronic lymphocytic leukaemia (CLL)". Cancer Research UK. 18 September 2020. Archived from the original on 23 October 2020. Retrieved 23 October 2020.
  4. ^
    American Association for Clinical Chemistry (12 August 2020). "Complete Blood Count (CBC)". Lab Tests Online. Archived
    from the original on 18 August 2020. Retrieved 8 September 2020.
  5. ^ a b c Smock, KJ. Chapter 1 in Greer, JP et al, ed. (2018), sec. "Advantages and sources of error with automated hematology".
  6. ^ a b Turgeon, ML (2016). p. 309.
  7. ^ Harmening, DM (2009). pp. 2–3.
  8. ^
    PMID 25676368
    .
  9. ^ a b Keohane, E et al. (2015). p. 244.
  10. PMID 24995446
    .
  11. ^ Marshall, WJ et al. (2014). p. 497.
  12. ^ a b c Van Leeuwen, AM; Bladh, ML (2019). p. 377.
  13. ^ Lewandrowski, K et al. (2016). p. 96.
  14. ABIM Foundation. American Association of Blood Banks. Archived from the original
    on 24 September 2014. Retrieved 12 July 2020.
  15. ^ a b Lewandrowski, K et al. (2016). p. 97.
  16. ^ Hartman, CJ; Kavoussi, LR (2017). pp. 4–5.
  17. PMID 28241909
    .
  18. ^ Walls, R et al. (2017). p. 130.
  19. ^ Walls, R et al. (2017). p. 219.
  20. ^ Walls, R et al. (2017). p. 199.
  21. ^ Walls, R et al. (2017). p. 1464.
  22. ^ Moore, EE et al. (2017). p. 162.
  23. ^ Lewis, SL et al. (2015). p. 280.
  24. S2CID 20375973
    .
  25. ^ Fatemi, SH; Clayton, PJ. (2016). p. 666.
  26. ^ Dooley, EK; Ringler, RL. (2012). pp. 20–21.
  27. ^ Keohane, E et al. (2015). pp. 834–835.
  28. ^ Schafermeyer, RW et al. (2018). pp. 467–468.
  29. ^ Smock, KJ. Chapter 1 in Greer, JP et al, ed. (2018), sec. "Introduction".
  30. ^ a b Kaushansky, K et al. (2015). p. 11.
  31. ^ Kaushansky, K et al. (2015). p. 43.
  32. ^ Kaushansky, K et al. (2015). pp. 42–44.
  33. ^ McPherson, RA; Pincus, MR (2017). p. 574.
  34. ^ Bain, BJ et al. (2017). p. 8.
  35. ^ a b Bain, BJ et al. (2017). p. 10.
  36. ^ Bain, BJ (2015). p. 213.
  37. ^ Keohane, E et al. (2015). p. 245.
  38. ^ a b Lewandrowski, K et al. (2016). pp. 96–97.
  39. ^ "Routine Preoperative Tests for Elective Surgery (NG45)". National Institute for Health and Care Excellence. 5 April 2016. Archived from the original on 28 July 2020. Retrieved 8 September 2020.
  40. ^ Kirkham, KR et al. (2016). p. 805.
  41. ^ Smock, KJ. Chapter 1 in Greer, JP et al, ed. (2018), sec. "Specimen collection".
  42. ^ Keohane, E et al. (2015). p. 28.
  43. ^ Bain, BJ et al. (2017). p. 1.
  44. ^ Smock, KJ. Chapter 1 in Greer, JP et al, ed. (2018), sec. "Cell counts", "Volume of packed red cells (hematocrit)", "Leukocyte differentials".
  45. ^ a b c d Bain, BJ et al. (2017). pp. 551–555.
  46. ^ Bain, BJ (2015). p. 29.
  47. ^ Dasgupta, A; Sepulveda, JL (2013). p. 305.
  48. ^
    PMID 25676376
    .
  49. ^ a b c Kottke-Marchant, K; Davis, B (2012). p. 8.
  50. ^ Shapiro, HM (2003). p. 1.
  51. ISSN 1943-7730
    .
  52. ^ Kaushansky, K et al. (2015). p. 12.
  53. ^ a b Bain, BJ et al. (2017). pp. 32–33.
  54. ^ McPherson, RA; Pincus, MR (2017). p. 44.
  55. ^ Bain, BJ (2015). pp. 29–30.
  56. PMID 31162693
    .
  57. ^ a b Smock, KJ. Chapter 1 in Greer, JP et al, ed. (2018), sec. "Hemoglobin concentration".
  58. ^ a b Keohane, E et al. (2015). p. 208.
  59. ^ Bain, BJ (2015). pp. 30–31.
  60. ^
    S2CID 113694419
    .
  61. ^ Keohane, E et al. (2015). pp. 208–209.
  62. ^ a b Bain, BJ et al. (2017). p. 32.
  63. ^ Keohane, E et al. (2015). pp. 210–211.
  64. ^ Keohane, E et al. (2015). p. 210.
  65. ^ Kottke-Marchant, K; Davis, B (2012). p. 27.
  66. ^ a b c d e Smock, KJ. Chapter 1 in Greer, JP et al, ed. (2018), sec. "Volume of packed red cells (hematocrit)".
  67. ^ Smock, KJ. Chapter 1 in Greer JP et al, ed. (2018), sec. "Mean corpuscular volume"; "Mean corpuscular hemoglobin"; "Mean corpuscular hemoglobin concentration"; "Red cell distribution width".
  68. ^ Keohane, E et al. (2015). p. 2.
  69. ^ Keohane, E et al. (2015). p. 209.
  70. ^ a b c Bain, BJ et al. (2017). p. 37.
  71. ^ Arneth, BM; Menschikowki, M. (2015). p. 3.
  72. ^ a b c Smock, KJ. Chapter 1 in Greer JP et al, ed. (2018), sec. "Leukocyte differentials".
  73. ^ Naeim, F et al. (2009). p. 210.
  74. ^ a b Turgeon, ML (2016). p. 318.
  75. ^ a b Bain, BJ et al. (2017). p. 39.
  76. ^ a b Smock, KJ. Chapter 1 in Greer, JP et al, ed. (2018), sec. "Introduction"; "Cell counts".
  77. ^
    PMID 23301216
    .
  78. ^ .
  79. ^ .
  80. ^ Bain, BJ et al. (2017). p. 43.
  81. ^ Keohane, E et al. (2015). p. 225.
  82. ^ Bain, BJ. (2015). pp. 9–11.
  83. ^ Palmer, L et al. (2015). pp. 288–289.
  84. ^ Turgeon, ML (2016). pp. 325–326.
  85. ^ Bain, BJ (2015). p. 98.
  86. ^ Bain, BJ (2015). p. 154.
  87. ^ Wang, SA; Hasserjian, RP (2018). p. 10.
  88. ^ a b Turgeon, ML (2016). p. 329.
  89. ^ a b d'Onofrio, G; Zini, G. (2014). p. 289.
  90. ^ Palmer, L et al. (2015). pp. 296–297.
  91. ^ a b c Keohane, E et al. (2015). p. 226.
  92. ^ a b Smock, KJ. Chapter 1 in Greer, JP et al, ed. (2018), sec. "Cell counts".
  93. ^ Keohane, E et al. (2017) p. 189.
  94. ^ Bain, BJ (2015). pp. 22–23.
  95. ^ Keohane, E et al. (2017). pp. 190–191.
  96. ^ Bain, BJ et al. (2017). pp. 19–22.
  97. ^ Bain, BJ et al. (2017). pp. 548–552.
  98. ^ Keohane, E et al. (2015). p. 46.
  99. ^
    PMID 27161194
    .
  100. ^ a b Kottke-Marchant, K; Davis, B (2012). pp. 697–698.
  101. PMID 31069974
    .
  102. ^ Greer, JP (2008). p. 4.
  103. ^ Kottke-Marchant, K; Davis, B (2012). p. 438.
  104. ^ Bain, BJ et al. (2017). pp. 539–540.
  105. S2CID 4978828
    .
  106. ^ Bain, BJ et al. (2017). p. 551.
  107. ^ Keohane, E et al. (2015). pp. 4–5.
  108. ^ Blann, A; Ahmed, N (2014). p. 106.
  109. ^ Turgeon, ML (2016). p. 293.
  110. ^ Bain, BJ et al. (2017). pp. 33–34.
  111. ^ Turgeon, ML (2016). pp. 319–320.
  112. PMID 27565952
    .
  113. ^ Keohane, E et al. (2015). p. 195.
  114. ^ a b Bain, BJ (2015). p. 22.
  115. ^ a b c d Keohane, E et al. (2015). p. 196.
  116. ^ Schmaier, AH; Lazarus, HM (2012). p. 25.
  117. ^ a b Bain, BJ (2015). pp. 73–75.
  118. ^
    PMID 30849034
    .
  119. ^ Keohane, E et al. (2015). p. 285.
  120. ^ Keohane, E et al. (2015). p. 286.
  121. ^ Kaushansky, K et al. (2015). p. 503.
  122. ^ Vieth, JT; Lane, DR (2014). pp. 11-12.
  123. ^ Bain, BJ (2015). p. 297.
  124. ^ DiGregorio, RV et al. (2014). pp. 491–493.
  125. ^ Isaacs, C et al. (2017). p. 331.
  126. ^ Bain, BJ (2015). p. 232.
  127. ^ McPherson, RA; Pincus, MR (2017). pp. 600–601.
  128. ^ a b Smock, KJ. Chapter 1 in Greer, JP et al, ed. (2018), sec. "Mean corpuscular hemoglobin concentration".
  129. ^ Keohane, E et al. (2015). p. 197.
  130. ^ a b Kottke-Marchant, K; Davis, B (2012). p. 88.
  131. ^ Bain, BJ (2015). p. 193.
  132. ^ Bain, BJ et al. (2017). pp. 501–502.
  133. ^ Ciesla, B (2018). p. 26.
  134. ^ Powell, DJ; Achebe, MO. (2016). pp. 530, 537–539.
  135. ^ Harmening, DM (2009). p. 380.
  136. ^ Pagana, TJ et al. (2014). p. 992.
  137. ^ Walls, R et al. (2017). pp. 1480–1481.
  138. ^ Territo, M (January 2020). "Overview of White Blood Cell Disorders". Merck Manuals Consumer Version. Archived from the original on 23 June 2020. Retrieved 8 September 2020.
  139. ^ Pagana, TJ et al. (2014). p. 991.
  140. ^ McCulloh, RJ; Opal, SM. Chapter 42 in Oropello, JM et al, ed. (2016), sec. "White blood cell count and differential".
  141. American Association for Clinical Chemistry (29 July 2020). "WBC Differential". Lab Tests Online. Archived
    from the original on 19 August 2020. Retrieved 8 September 2020.
  142. ^ Wang, SA; Hasserjian, RP (2018). p. 8.
  143. ^ Palmer, L et al. (2015). pp. 294–295.
  144. ^ Chabot-Richards, DS; George, TI (2015). p. 10.
  145. ^ Palmer, L et al. (2015). p. 294.
  146. ^ Turgeon, ML (2016). p. 306.
  147. ^ a b Kaushansky, K et al. (2015). p. 44.
  148. ^ Hoffman, EJ et al. (2013). p. 644.
  149. ^ Porwit, A et al. (2011). pp. 247–252.
  150. ^ Walls, R et al. (2017). p. 1483.
  151. ^ Walls, R et al. (2017). pp. 1497–1498.
  152. ^ Bain, BJ (2015). p. 99.
  153. ^ Bain, BJ et al. (2017). p. 85.
  154. ^ Bain, BJ et al. (2017). p. 498.
  155. ^ Bain, BJ (2015). p. 243.
  156. ^ Porwit, A et al. (2011). p. 256.
  157. ^ Palmer, L et al. (2015). p. 298.
  158. ^ Turgeon, ML (2016). pp. 358–360.
  159. ^ Kaushansky, K et al. (2015). p. 1993.
  160. ^ Turgeon, ML (2016). p. 315.
  161. ^ Walls, R et al. (2017). pp. 1486–1488.
  162. PMID 25383671
    .
  163. ^ a b Keohane, E et al. (2015). p. 4.
  164. ^ Walls, R et al. (2017). p. 1489.
  165. ^ Gersten, T (25 August 2020). "Platelet count: MedlinePlus Medical Encyclopedia". MedlinePlus. United States National Library of Medicine. Archived from the original on 9 September 2020. Retrieved 9 September 2020.
  166. ^ Wang, SA; Hasserjian, RP (2018). p. 7.
  167. ^ Kaushansky, K et al. (2015). pp. 18–19.
  168. ^ a b Kaushansky, K et al. (2015). p. 14.
  169. ^ Turgeon, ML (2016). pp. 318–319.
  170. ^ Turgeon, ML (2016). p. 319.
  171. ^ a b c d Kaushansky, K et al. (2015). p. 16.
  172. ^ Bain, BJ et al. (2017). pp. 42–43.
  173. ^ Harmening, DM (2009). pp. 8–10.
  174. .
  175. ^ Zandecki, M et al. (2007). pp. 24–25.
  176. PMID 30267430
    .
  177. ^ Bain, BJ (2015). p. 90.
  178. ^ a b Keohane, E et al. (2015). Front matter.
  179. ^ Bain, BJ (2015). pp. 211–213.
  180. ^ Bain, BJ (2015). pp. 211–213.
  181. ^ a b c Bain, BJ (2015). p. 143.
  182. ^ Lanzkowsky, P et al. (2016). p. 197.
  183. ^ Kaushansky, K et al. (2015). p. 99.
  184. ^ Kaushansky, K et al. (2015). p. 103.
  185. ^ Bain, BJ (2015). p. 220.
  186. ^ Bain, BJ (2015). p. 214.
  187. ^ Bain, BJ et al. (2017). pp. 8–10.
  188. ^ Palmer, L et al. (2015). p. 296.
  189. ^ Bain, BJ (2015). p. 195.
  190. ^ Kottke-Marchant, K; Davis, B (2012). p. 67.
  191. ^ Bain, BJ (2015). p. 194.
  192. ^ Turgeon, ML (2016). p. 91.
  193. ^ Kottke-Marchant, K; Davis, B (2012) pp. 80, 86–87.
  194. ^ Bain, BJ (2015). pp. 196–197.
  195. PMID 35470271
    .
  196. ^ Rodak, BF; Carr, JH. (2013). p. 109.
  197. ^ Wang, SA; Hasserjian, RP (2018). p. 9.
  198. ^ Kottke-Marchant, K; Davis, B (2012). pp. 19–20.
  199. ^ Science Museum, London. "Haemoglobinometer, United Kingdom, 1850–1950". Wellcome Collection. Archived from the original on 29 March 2020. Retrieved 29 March 2020.
  200. ^ Keohane, E et al. (2015). pp. 1–4.
  201. ^ Kottke-Marchant, K; Davis, B. (2012). p. 1.
  202. ^ Wintrobe, MM. (1985). p. 10.
  203. ^ a b Kottke-Marchant, K; Davis, B. (2012). pp. 3–4.
  204. PMID 14139094
    .
  205. ^ .
  206. ^ Davis, JD (1995). p. 167.
  207. ^ Kottke-Marchant, K; Davis, B (2012). p. 4.
  208. ^ Davis, JD (1995). pp. 168–171.
  209. S2CID 37401579
    .
  210. ^ Keohane, E et al. (2015). p. 134.
  211. ^ a b c d Kottke-Marchant, K; Davis, B (2012). p. 5.
  212. PMID 23596093
    .
  213. ^ .
  214. ^ Kottke-Marchant, K; Davis, B (2012). p. 6.
  215. ^ Groner, W (1995). pp. 12–14.
  216. S2CID 31055044
    .
  217. ^ Da Costa, L (2015). p. 5.
  218. ^ Groner, W (1995). pp. 12–15.
  219. PMID 2271793
    .
  220. .
  221. ^ Da Costa, L (2015). pp. 5–6.
  222. ^ McCann, SR (2016). p. 193.
  223. ^ Melamed, M (2001). pp. 5–6.
  224. ^ Shapiro, HM (2003). pp. 84–85.
  225. ^ a b Melamed, M. (2001). p. 8.
  226. ^ Picot, J et al. (2012). p. 110.
  227. PMID 4137312
    .
  228. ^ Pierre, RV (2002). p. 281.
  229. ^ Kottke-Marchant, K; Davis, B (2012). pp. 8–9.

General bibliography