The "Thal-index" with the BTT prediction, exe to discriminate Beta thalassaemia traits from other microcytic anaemias

Abstract

INTRODUCTION AND OBJECTIVES: Attempts have been made previously to differentiate beta-thalassaeima 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. METHODs: The study was carried out prospectively from November 2008 to March 2010 using 326 randomly collected blood samples with a mean-cell volume (MCV) of less than 80 fi. HbA2 measured by HPLC was used to diagnose BTT. We used Fishers step wise linear discriminant function analysis to develop an algorithm with RC parameters. Calculated new index "Thai-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). RESULTS: New index, referred to as the "Thai-index", was calculated using discriminant function analysis and is given as "Thai-index" = [(0.615 x MCV) + (0.518 x MCH) + (0.446 x ROW)]. A value of 59 for "Thai-index" has 90% sensitivity and 85% specificity for differentiating BTT from other microcytic anaemias. CONCLUSIONS: This showed better sensitivity and specificity compared to other formulae presently used (i.e Mentzer in Eshani et al). Although this cannot replace HPLC, BTTprediction.exe is useful for quick prediction and is the first computer programme available for this function.