An “on the spot” test for targeted screening in index families of thalassaemia

Objective: To assess the usefulness of One Tube Osmotic Fragility Test (OTOFT) for on the spot screening of rural families with history of thalassaemia. Methods: It was an observational cross-sectional study conducted at Pathology Department of PNS Shifa Hospital, Karachi and included all available members of three families from the rural district (Badin) in Pakistan with history of at least one child with thalassaemia major. One drop of finger prick blood was added to 5 ml of 0.36% saline in a test tube (diameter 2cm). The results were read after 5-10 minutes by visualizing a written material through the contents of the test tube. In addition, samples were also collected for blood counts, Hb electrophoresis and serum ferritin. Results: OTOFT was positive in 135/171 (79%) subjects. In the 135 positives, subsequent investigations showed that 61 (45%) had thalassaemia trait, 52 (39%) had iron deficiency and 22 (16%) had neither of the two and were considered false positive. In the 35 OTOFT negative subjects none had thalassaemia trait while only one had iron deficiency (false negative). Conclusions: OTOFT is a simple and cost effective test which can be used in the field for screening index families with thalassaemia. While a positive test is sensitive for detection of thalassaemia or iron deficiency an OTOFT negative individual may be excluded from further testing for thalassaemia.