Study of discriminant factor M/H ratio in screening for β thalassemia trait

Introduction: Beta Thalassemia syndrome is a group of hereditary disorders characterized by genetic deficiency in the synthesis of beta globin chains located on chromosome 11. A major diagnostic challenge is to differentiate between mild microcytic hypochromic anaemia due to BTT from other causes such as iron deficiency (IDA), sideroblastic anaemia etc. The microcytic to hypochromic ratio (M/H ratio) is one of the simplest discriminant functions which is based on the fact that in Iron deficiency anaemia the RBCs are more hypochromic as compared to thalassemia trait. The present study was carried out in our diagnostic centre with the aim of evaluating the M/H ratio for screening patients for BTT. Materials and Methods: This was a retrospective study carried out on a total of 200 patients between January to April 2018 coming to our diagnostic centre for complete blood count and Hb electrophoresis for evaluating the M/H ratio to screen for BTT. HbA2 > 3.5% was considered to be diagnostic of BTT. M/H ratio as an indicator of differentiating between BTT and IDA was compared with other discriminant factors like England & Fraser, Mentzer Index, Shine & Lal Index and Shrivastava Index. Results: There were 73 (36.5%) male and 127 (63.5%) females with a M:F ratio of 0.57:1. Out of 200 patients, 22 (11%) patients were diagnosed as BTT. Of these M/H ratio was <0.9 in 5 (22%) patients while >0.9 in 11 (77.27%) patients. England and Fraser index had highest specificity (94%) with a sensitivity of 23%. Shine and Lal had a specificity of 39% and sensitivity of 95%, Mentzer had a specificity of 83% and sensitivity of 45%, Srivastava had sensitivity and specificity of 36% and 78% respectively while M/H ratio had specificity (70%) and sensitivity (77%). Conclusion: M/H ratio provided by Advia 2120 hematology analyzer is as effective as preliminary screening tool for selection of samples for HbA2 estimation. It is a rapid, automated formula provided without any additional cost to the patient.