Using Osmotic Fragility Test in Combination with Red Blood Cell Indices for Screening of Severe Thalassemia Traits

Abstract

Screening of severe thalassemia trait aims to reduce workload and cost of confirmation. Screening by using osmotic fragility test (OF) or red blood cell indices (mean corpuscular volume (MCV)/mean corpuscular hemoglobin (MCH)) is generally a strategy of choice. However, several laboratories use OF test in combination with MCV/MCH as an alternative strategy to increase efficiency of screening of β-thalassemia traits and α-thalassemia 1 traits. The objective of this research was to evaluate the results of screening strategy by using both OF test and MCV/MCH in comparison with those using either OF test or MCV/MCH. Retrospective data of OF test and MCV/MCH along with hemoglobin typing and relative quantitative PCR results of pregnant women and husbands from 8 hospitals in Chiang Mai, Nan and Lamphun from 2016 to 2018, were analyzed. The results showed that, out of 1,126 cases, 31.98% were positive by OF but had normal MCV/MCH. Results of hemoglobin typing and relative quantitative PCR of all cases revealed that 24.24% were diagnosed with β-thalassemia traits and/or α-thalassemia 1 traits. However, only 0.27% (3 cases) were positive by OF but had normal MCV/ MCH. By using only MCV/MCH, the number of assessed at-risk couples was 61, one couple less than those screened by using both OF test and MCV/MCH. This couple, the pregnant woman showed normal MCV/MCH and A2A Hb typing with borderline Hb A2 level (3.6%), thecharacteristic of which has never been reported in severe thalassemia traits. The study suggestedthat OF test, which showed high false positive rate, in combination with MCV/MCH is of little use for screening of severe thalassemia trait. On the contrary, the use of this strategy is likely to increase workload and cost not only for screening but also for confirmation.