Evaluation of single‐tube osmotic fragility as a screening test for thalassemia

A single‐tube osmotic fragility test has been proposed for thalassemia screening with a range of different concentrations of saline having been employed. We have compared the sensitivity and specificity of 0.32%, 0.34%, and 0.36% buffered saline, and on the basis of our findings, recommend the use of 0.36% saline. This gave definitely positive or equivocal results in 81 of 85 patients with β thalassemia trait and in 4 of 4 with α 0 thalassemia trait. There were 14% false positive results in hematologically normal patients and 81% of the samples from patients with various variant hemoglobins gave positive results. The sensitivity was 95% and specificity 86%. The single‐tube osmotic fragility test is potentially useful in under‐resourced laboratories although it cannot replace automated red cell indices using electronic counters. Am. J. Hematol. 79:198–201, 2005. © 2005 Wiley‐Liss, Inc.