Background: β-thalassemia trait (BTT) can be screened by several discriminator indices (DIs) using complete blood counts (CBC). These DIs can help differentiate BTT from other causes of anaemia, thus reducing the financial burden of laboratory testing. At standard cut-off values, statistical analyses traditionally used to compare the diagnostic competence of these DIs give variable results. This study establishes new optimal cut-off values to improve the applicability of these DIs for BTT screening.
Methods: This was a retrospective study conducted on anaemic adults whose high-performance liquid chromatography (HPLC) and CBC results achieved over the past 6 months were reviewed. Based on HPLC reports, patients were categorised into BTT and non-BTT groups, with each group comprising 25 age- and sex-matched patients. Discriminator indices, including Mentzer’s Index (MI), Green and King Index (GKI), Sehgal Index (SI), Shine and Lal Index (SLI), Srivastava Index (SrI), and England and Fraser Index (EFI), were calculated for both groups. Statistical analysis was performed respective to standard cut-off values to establish new optimal cut-off values with the highest sensitivity and specificity.
Results: According to the results, SrI emerged as the best index, offering high sensitivity, specificity, Youden’s Index, accuracy, and odds ratio. On the other side, SLI and GKI were observed to be poor indices with low sensitivity and specificity. The new optimal cut-off values for the best performance of each DI for BTT screening were as follows: SrI ≤3.5, MI ≤11.4, GKI ≤59.7, SI ≤709.4, SLI ≤941.1, and EFI ≤1.91.
Conclusion: The performance of DIs at standard cut-off values was poor to screen BTT. New optimal cut-off values provided maximal sensitivity and specificity thereby enhancing their performance as screening parameters for BTT in regions with a high-prevalence of the condition. Further studies are warranted to substantiate the new cut-off values for BTT screening.
