Screening for beta-thalassemia trait; applicability of red cell indices and parameters – A study in Sri Lanka

OBJECTIVE: Red cell indices and parameters are used to screen beta-thalassemia trait (BTT). Different red cell indices and formulae used to discriminate BTT in different populations show inconsistent results. METHODS: A retrospective study was performed to assess reliability of 11 red cell indices, parameters and formulae in differentiating BTT from non-BTT in a cohort of individuals referred for confirmation of BTT. RESULTS: Of 111 individuals, 79 were females and 32 were males. Of the total, 89 were confirmed to have BTT by Hb A2 quantification. The mean age of the group was 29.9 ± 19.2 years. The mean Hb concentration, MCV and MCH in BTT group were 10.45 ± 1.6 g/dL, 62.1 ± 5.4 fl, and 19.7 ± 1.7 pg, respectively. The mean red cell count in BTT group was 5.3 ± 0.8 × 10(9)/L while in non BTT group it was 4.7 ± 0.7 × 10(9)/L. The highest specificity (86.4%) was shown by Sirdah, Sriwastava and England and Fraser indices, but their sensitivities were 61.8%, 57.3%, and 32.6%. The lowest number of false positives (n = 3, 13.6%) was shown by Srivastava, Sirdah and England and Fraser indices. Shine and Lal index showed 100% sensitivity and NPV and 12 false positives. MCV and MCH showed results similar to Shine and Lal index with 16 false positives each. CONCLUSION: Use of Shine and Lal index in screening programs of BTT is superior to all the other indices and formulae. To confirm the findings of this study, further studies are recommended to be carried out in Sri Lanka on different ethnicities.