Validity of Nestroft in screening and diagnosis of beta-thalassemia trait

Validity of naked eye single tube red cell osmotic fragility test ('Nestroft') was evaluated on 253 individuals divided into two groups. The HbA2 values estimated in each child was taken as gold standard. Group I comprised of 93 individuals belonging to families in which at least one of the children was suffering from beta-thalassemia major and group II consisted of 160 normal children. The sensitivity of 'Nestroft' was 95.59 per cent (grp I) & 85.71 per cent (grp II), specificity was 84.2 per cent (grp I) and 81.7 per cent (grp II) with a negative predictive value as high as 99.21 per cent in general population. The results of the test were assessed by two independent observers and P values of 0.75 and 0.69 were found in grp I and grp II, respectively. The values clearly showed that the interobserver variation was statistically insignificant thus proving it to be an objective test. Comparative analysis of 'nestroft' with red cell indices, i.e. MCV (< 70 fi) and RBC count (> 4.5 x 10(12)/l) revealed it to be the most sensitive and specific test. 'Nestroft' has emerged as the single most effective, inexpensive and easily reproducible test of population screening for beta-thalassemia trait.