Screening Beta Thalassemia Trait- Performance Evaluation of Discriminator Indices

摘要

Introduction: Beta Thalassemia Trait (BTT) is the most common haemoglobinopathy worldwide. High Performance Liquid Chromatography (HPLC) is the technique of choice for diagnosis. However, it is expensive and there is a need to triage patients for HPLC in resource limited nations. Various discriminator indices are used for the same purpose. Aim: To compare the utility of 11 different discriminator indices for differentiating between Iron Deficiency Anaemia (IDA) and BTT. Materials and Methods: The present study was a retrospective observational study done at Maulana Azad Medical College, Delhi, India over a period of one year (January 2017-January 2018). A total of 510 cases with clinically suspected haemoglobinopathy or with microcytic hypochromic anaemia along with relative erythrocytosis were analysed. After noting clinical details, data regarding haemogram findings, iron parameters and serum vitamin B12 and folate levels were collected. An Haemoglobin A2 (HbA2) value of 3.8-8% was used for confirming diagnosis of BTT. Eleven discriminator indices prediciting BTT were calculated and their utility was assessed by calculating the sensitivity, specificity, Positive Predictive Value (PPV), Negative Predictive Value (NPV) and Youden’s index. The statistical analysis was done using Statistical Package for the Social Sciences (SPSS) 16 software. Results: Out of total 510 cases, 149 (29.2%) were confirmed as BTT. Green and King index had the maximum sensitivity (67.1%) and Shine-Lal index had maximum specificity (91.1%) for diagnosing BTT. Green and King index also had the best Youden’s index (43.9%). Conclusion: Cell counter based formulas are cheaper, easy to calculate and reliable tools for screening BTT suspected cases which can be further confirmed by more specific tests like HPLC and electrophoresis. The authors found Mean Corpuscular Haemoglobin (MCH), Mean Corpuscular Haemoglobin Concentration (MCHC) and Red Blood Cell (RBC) count as the most useful for selecting patients for more specific tests. The Green and King index was found to be most reliable for predicting BTT in the present study.