Abstract
Introduction: Detection of beta-thalassemia trait or carriers (beta-TT) depends significantly on an increase in Hemoglobin A(2) (HbA(2)) levels, which is found at low levels (<3%) in normal healthy individuals and elevated levels (>= 3.5%) in b-TT individuals. The study was designed to evaluate the reliability of the diagnostic parameter HbA(2) in the differentiation of beta-TT and non-beta-TT in Saudis.
Methods: The widely used high performance liquid chromatography (Variant II Bio-Rad) was used to measure HbA(2) levels in blood. Sanger sequencing was used to screen the variation in globin genes (HBB, HBD, HBA(1), and HBA(2)). All the study subjects were divided into beta TT and non-beta TT (wild) categories based on the presence or absence of HBB variations and further sub-divided into false positive, true positive, false negative, and true negative, based on HbA(2) values.
Results: Out of 288 samples, 96 had HBB gene mutations. Of the 96 beta-TT samples, sickle cell trait (SCT) samples (n = 58) were excluded, while the remaining (38 beta-TT) were included in the detailed analysis: seven subjects with the HBB mutation had normal HbA(2) (<3%), and three were borderline (3.1-3.9%). The remainder (n = 28) had an elevated HbA(2) level (>4%). Based on HbA(2) analysis alone, both these groups would be incorrectly diagnosed as normal. Similarly, of the 189 non-beta-TT samples, 179 had normal HbA(2), eight had borderline HbA(2), and two had a HbA(2) level above 4%. Based on HbA(2) analysis alone, borderline and >4% HbA(2) individuals, negative for b-TT, can be incorrectly diagnosed as carriers.
Conclusion: Given the percentage of samples falling in the HbA(2) "borderline" and "normal" categories, it can be concluded that HbA(2) has a measure of unreliability in the diagnosis of beta-thalassemia carriers.