The Thal-Index with the BTT Prediction.exe to Discriminate β-Thalassaemia Traits from Other Microcytic Anaemias

Several attempts have been made previously to differentiate β-thalassaemia trait (BTT) from other microcytic anaemias using formulae with red cell (RC) parameters. Presently available formulae have low sensitivity and specificity. We wanted to develop a more precise algorithm, which could be used in situations where the gold-standard test for thalassaemia diagnosis: the high performance liquid chromatography (HPLC) is not available. The study was carried out prospectively from November 2008 to March 2010 from randomly collected blood samples with a mean cell volume (MCV) of less than 80 fL. HbA2 measured by HPLC was used to diagnose BTT. We used Fishers stepwise linear discriminant function analysis to develop an algorithm with RC parameters. Calculated new index Thal-index was then subjected to receiver operating characteristic curve analysis to identify best cutoff to discriminate BTT from other microcytic blood films. Software was developed to predict the BTT status (BTT prediction.exe). New index, referred to as the Thal-index, was calculated using discriminant function analysis and is given as Thal-index = [(0.615 x MCV) + (0.518 x mean corpuscular hemoglobin) + (0.446 x red cell distribution width)]. A value of 59 for Thal-index has 90% sensitivity and 85% specificity for differentiating BTT from other microcytic anaemias. This showed better sensitivity and specificity compared to other formulae presently used (i.e., Mentzer in Eshani, et al.). Our study gives a better answer to set-up where HPLC is not available. Although this cannot replace HPLC, BTT prediction.exe is useful to predict instantly and is the first ever computer program available for this function.