Partial thromboplastin time
Partial thromboplastin time | |
---|---|
Other names | Activated partial thromboplastin time; Activated partial prothrombin time; Activated partial thrombin time |
MeSH | D010314 |
The partial thromboplastin time (PTT), also known as the activated partial thromboplastin time (aPTT or APTT), is a blood test that characterizes coagulation of the blood. A historical name for this measure is the kaolin-cephalin clotting time (KCCT),[1] reflecting kaolin and cephalin as materials historically used in the test. Apart from detecting abnormalities in blood clotting,[2] partial thromboplastin time is also used to monitor the treatment effect of heparin, a widely prescribed drug that reduces blood's tendency to clot.
The PTT measures the overall speed at which blood clots form by means of two consecutive series of biochemical reactions known as the
The PTT is often used in conjunction with another measure of how quickly blood clotting takes place called the prothrombin time (PT). The PT measures the speed of clotting by means of the extrinsic pathway and common pathway.
Methodology
Partial thromboplastin time is typically analyzed by a
- Blood is drawn into a citrate, molecules which act as an anticoagulant by binding the calcium in a sample. The blood is mixed, then centrifuged to separate blood cells from plasma (as partial thromboplastin time is most commonly measured using blood plasma).
- A sample of the plasma is extracted from the test tube and placed into a measuring test tube.
- Next, an excess of calcium (in a phospholipid suspension) is mixed into the plasma sample (to reverse the anticoagulant effect of the oxalate enabling the blood to clot again).
- Finally, in order to activate the ictericsamples.
Interpretation
The typical reference range is between 25 seconds and 33 s (depending on laboratory). Longer times of up to 50 s do apply to infants. Shortening of the PTT is considered to have little clinical relevance, but some research indicates that it might increase risk of thromboembolism.[3] Normal PTT requires the presence of the following coagulation factors: I, II, V, VIII, IX, X, XI and XII. Notably, deficiencies in factors VII or XIII will not be detected with the PTT test.[citation needed]
Prolonged aPTT may indicate:[citation needed]
- use of heparin (or contamination of the sample)
- antiphospholipid antibody (especially lupus anticoagulant, which paradoxically increases propensity to thrombosis)
- coagulation factor deficiency (e.g., hemophilia)
- sepsis — coagulation factor consumption
- presence of antibodiesagainst coagulation factors (factor inhibitors)
To distinguish the above causes,
The aPTT is usually normal in pregnancy but tends to slightly decrease in late pregnancy.[4]
aPTT-based APC resistance test
The aPTT-based
History
The PTT was first described in 1953 by researchers at the University of North Carolina at Chapel Hill.[8] This is the reason why the color of the Vacutainer tube top is Carolina blue.[citation needed]
See also
References
- ^ "KCCT - General Practice Notebook". GP Notebook. Oxbridge Solutions Ltd. Retrieved 2010-06-08.
- ^ "MedlinePlus Medical Encyclopedia: Partial thromboplastin time (PTT)". Retrieved 2009-01-01.
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- ^ PMID 29162399.
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