Mentzer Index with RCDW as a High-Specificity Screening Tool for Differentiating Iron Deficiency Anemia from Beta-Thalassemia Trait

Abstract

Background: Differentiating iron deficiency anemia (IDA) from beta-thalassemia trait (BTT) remains challenging in clinical practice, often requiring expensive confirmatory tests. This study evaluated the diagnostic performance of the Mentzer Index combined with red cell distribution width (RDW) for discriminating between these conditions.

Methods: This cross-sectional diagnostic accuracy study enrolled 200 patients with microcytic anemia (MCV <80 fL), including 120 with confirmed IDA and 80 with BTT. Complete blood count parameters were analysed, and the Mentzer Index was calculated as MCV/RBC count. IDA diagnosis required ferritin <30-40 ng/mL and additional iron study abnormalities, while BTT required HbA₂ >3.5% by HPLC. Combined criteria defined IDA as Mentzer Index ≥13 AND RDW >15%, and BTT as Mentzer Index <13 AND RDW ≤15%. Diagnostic performance metrics, including sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy, were calculated.

Results: IDA patients demonstrated significantly higher Mentzer Index (16.7±2.3 vs 10.7±1.5, p<0.001) and RDW (18.4±2.1% vs 13.2±1.4%, p<0.001) compared to BTT patients. The Mentzer Index alone achieved 88.5% accuracy, 89.2% sensitivity, and 87.5% specificity. The combined approach significantly improved performance, achieving 93.5% accuracy, 91.7% sensitivity, and 96.3% specificity. Specificity increased by 8.8 percentage points, with the false positive rate reduced by 70% (from 12.5% to 3.7%). PPV improved from 91.5% to 97.3%.

Conclusion: Combining the Mentzer Index with RDW provides superior diagnostic accuracy for differentiating IDA from BTT, particularly improving specificity and reducing misclassification. This cost-effective screening approach using routine CBC parameters can correctly classify 93.5% of patients, potentially reducing unnecessary confirmatory testing by approximately 90% while maintaining high diagnostic confidence.