One tube osmotic fragility test: a screening test for microcytic red cells

ABSTRACT

To evaluate the usefulness of One Tube Osmotic Fragility Test [OTOFT] for detection of microcytosis. Validation study. The study was carried out from July 2004 to November 2004 at Pathology Department PNS Shifa, Karachi. Five hundred and fifteen individuals were studied who reported to the reception of Pathology Dept. for blood complete picture. One drop of finger prick blood was added to a test tube containing 5 ml of 0.36% saline. The results were read at 10 minutes interval by visualizing a written material through the contents of the test tube. Three ml of blood was collected in the EDTA tube by venepuncture for determination of Haemoglobin [Hb], Mean Cell Volume [MCV] and Mean Cell Haemoglobin [MCH] by electronic haematology counter "Sysmex 4500". Out of total 515 subjects studied, OTOFT was positive in 130 [25.2%] and negative in 385 [74.8%] cases. OTOFT positive and negative groups revealed statistically significant difference [P-value of < 0.05] in MCV, MCH and Hb. OTOFT proved to be 92.5% sensitive and 95.2% specific for screening of microcytosis. It had positive predictive value of 85.38% and negative predictive value was 97.66%. The diagnostic accuracy was 94.6%. One Tube Osmotic Fragility Test [OTOFT] is a simple and cost effective test, which is highly sensitive as well as specific for screening of microcytosis. It may prove a useful tool in targeted and/or population screening for thalassaemia