Hemoglobin Barts
Hemoglobin Barts, abbreviated Hb Barts, is an abnormal type of
Since hemoglobin Barts is elevated in alpha thalassemia, it can be measured, providing a useful screening test for this disease in some populations.[3]
The ability to measure hemoglobin Barts makes it useful in newborn screening tests. If hemoglobin Barts is detected on a newborn screen, the patient is usually referred for further evaluation since detection of hemoglobin Barts can indicate either one alpha globin gene deletion, making the baby a silent alpha thalassemia carrier, two alpha globin gene deletions (alpha thalassemia), or
Genotypes | Alpha-Globin Gene Deletions | Clinical Component |
αα/αα | 0 | Normal |
-α/αα | 1 | Silent Carrier |
--/αα or -α/-α | 2 | Alpha-Thalassemia Trait |
--/-α | 3 | Hb H Disease |
--/-- | 4 | Fetal Hydrops |
Table 1: α represents the presence of α-globin gene and- represents the deletion of α-globin gene.[6]
The chance of a fetus developing Hemoglobin Bart's hydrops fetalis is dependent upon if one or both parent carries the alpha-thalassemia trait. Due to this disease being incompatible with life, diagnosis for it is done prenatally.[7] Early detection of Hemoglobin (Hb) Bart's disease before the development of hydrops fetalis is crucial because fetuses that develop hydrops fetalis will either be stillborn or may die shortly after birth. There can be early pregnancy termination to prevent serious complications for the baby or mother. Studies shows that in 11 to 14 weeks of gestation, sonographic markers can associate affected from unaffected pregnancies. It was found that the most sensitive marker was CT ratio and MCA‐PSV.[8]
Parents at risk of having a child with Fetal Hydrops can continue their pregnancy with regular ultrasounds and intrauterine blood transfusion. Babies of such parents are born with no edema or major neurological defects, and eventually, this disease can be cured with Haematopoietic Stem Cell Transplantation. A newly developed diagnostic test, called Immunochromatography (IC) Strip Tests, uses monoclonal antibodies to detect Hemoglobin Barts in red blood cells' lysate. This diagnostic test is validated for positive and negative predictive values. It is also cheap and easy, making regular screening for alpha-thalassemia a plausible possibility.[9][10]
Anemia is a factor in fetuses with Hemoglobin Bart's disease as there is an "increased cardiac output" and hypovolemia as the tissues of the fetus require oxygen because of the gamma globulin's high affinity for oxygen. This deprives the tissues of receiving oxygen to function well. The symptoms of anemia occur within the first trimester.[11]
This variant of hemoglobin is so called as it was discovered at St Bartholomew's Hospital in London, often abbreviated to Barts.[12]
Notes
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- ^ "Pathophysiology of alpha thalassemia". www.uptodate.com. Retrieved 2016-08-30.
- PMID 10471652.
- PMID 28057638.
- ^ Songdej, Duantida; Babbs, Christian; Higgs, Douglas R. (March 9, 2017). "An international registry of survivors with Hb Bart's hydrops fetalis syndrome". ashpublications.org.
- S2CID 4349631.
- S2CID 40335193.
- S2CID 37146677.
- S2CID 247157134.
- PMID 31661492.
- PMID 25770840.
- PMID 13523233.