The test was false positive in 41 (9.1%) of 455 normal subjects while of 438 confirmed heterozygotes with beta-thalassaemia it was positive in 431 (98%) and negative in only seven (2%). The test was also found to be positive in 80% of patients with iron deficiency anaemia and alpha-thalassaemia trait, in 68% of patients with Hb E trait, in 40% of patients with Hb S trait, and in 78% of heterozygotes with rare haemoglobin variants. The increased sensitivity and effectiveness of 0.36% saline in detecting beta-thalassaemia trait and other disorders influencing osmotic fragility as compared to 0.32% saline and tyrode solutions was also confirmed in a study of 384 unselected schoolchild
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