Erythrocyte osmotic fragility test for screening of alpha‐thalassemia‐1 and beta‐thalassemia trait in pregnancy

Objectives : To evaluate the sensitivity and specificity of osmotic fragility test (OFT) as a screening test in predicting the severe thalassemia trait (α‐thalassemia‐1 & β‐thalassemia). Methods : A descriptive analysis and diagnostic test of non‐anemic pregnant women attending antenatal care clinic, Maharaj Nakorn Chiang Mai, during April, and July 2002 was made. Blood samples were collected from 446 singleton pregnancies with no obvious medical complication such as iron deficiency anemia. OFT was performed in the same day, using 0.45% glycerin saline solution and the cut‐off value of less than 60% was used for an abnormal test. Quantitative HbA2 test and PCR (SEA type) were done as a gold standard to confirm the diagnosis of β‐thalassemia trait and α‐thalassemia‐1 trait, respectively. Results : The main outcome measures were sensitivity, specificity, positive and negative predictive value of OFT. If the OFT cut‐off value of less than 60% was considered positive, the test had a sensitivity, specificity, positive and negative predictive value of 97.6%, 72.9%, 33.6%, and 99.5%, respectively. Conclusion : OFT has high sensitivity in detection of α‐thalassemia‐1 trait or β‐thalassemia trait and due to its simplicity with very low cost it may, therefore, be considered as a screening test in a wide population.