A modified osmotic fragility test (O.F.T.) : an alternative for screening for hemoglobinopathies

Abstract

Objectives: (1) to prove that the modified O.F.T. visualized by the button formation of unlysed erythrocytes has a good diagnostic performance to detect hemoglobinopathies (a thalassemia trait, thalassemia trait and hemoglobin E trait) ; (2) to compare diagnostic performance of the modified and the previous O.F.T.; (3) to investigate factors that may influence test performance of the modified O.F.T. Study design : descriptive, cross-sectional study. Methodology : 468 volunteers were involved in this study. Each volunteer was tested by both the modified and the previous O.F.T. by different laboratory technician. Each test was validated blindly and separately by a standard screening procedure. Then, diagnostic performance of each test as a result from computation by using 2x2 table were compared to each other. Total bilirubin level that may influence test performance was also observed. Results : It was found 51 cases of hemoglobinopathy, consisted of 12 cases of thalassemia trait and 39 cases of hemoglobin E trait. The other (417 volunteers) were classified into non-hemoglobinopathy group. Diagnostic performance of the modified O.F.T. is as follows : sensitivity is 86.3%; specificity is 75.3%; positive and negative predictive values are respectively 29.9% and 97.8% as well as accuracy is 76.5%. In term of detection rate both the modified O.F.T. and the previous O.F.T. are significantly different (p<0.05). The previous O.F.T. has a higher sensitivity i.e. 88.2%. However, the other test characteristics show that the modified test is better. Total bilirubin level up to 3.3 mg/dl. Does not show any different compared with its normal level to influence the test result (p>0.05).