Population screening for beta-thalassaemia.

The graphic recording of time to 50% haemolysis in a glycerine-saline solution is a simple, reproducible method of determining erythrocyte osmotic fragility. Studies on a normal population yielded an upper limit of normal of 90 s. In 250 healthy males from Northern Thailand all 19 with beta-thalassaemia minor had abnormal osmotic indices, and the value of the test was confirmed in beta-thalassaemia heterozygotes in Europe. Of 23 patients with iron deficiency 18 had abnormal osmotic indices. However, this is not thought likely to be a significant source of false positives in the screening of populations at risk of haemoglobinopathies but in whom iron deficiency is rare.