# Diagnostic Accuracy of the Patra Index and Red Cell Distribution Width Index in Distinguishing Beta-Thalassemia Trait From Iron Deficiency Anemia: A Retrospective Comparative Study

## TL;DR

This study compares two blood indices to help doctors tell apart beta-thalassemia trait from iron deficiency anemia, finding one to be highly specific but not perfect.

## Contribution

The study evaluates the Patra index and RDWI as diagnostic tools for differentiating BTT from IDA in a real-world clinical setting.

## Key findings

- The Patra index had 100% specificity and 83% sensitivity for identifying beta-thalassemia trait.
- RDWI showed 100% sensitivity but only 81.55% specificity for the same condition.
- The Patra index had a higher overall diagnostic accuracy (94.23%) compared to RDWI (87.82%).

## Abstract

Background

Distinguishing beta-thalassemia trait (BTT) from iron deficiency anemia (IDA) remains a clinical challenge, particularly in resource-limited settings where nutritional anemia is highly prevalent. This study aimed to compare the diagnostic accuracy of the Patra index with the red cell distribution width index (RDWI) for differentiating BTT from IDA, using high-performance liquid chromatography (HPLC) and serum ferritin as reference standards.

Methods

This retrospective diagnostic accuracy study was conducted at Rajendra Institute of Medical Sciences, Ranchi, India. A total of 156 patients diagnosed with either BTT or IDA were included. BTT was defined as hemoglobin A2 (HbA2) > 3.5%, and IDA as serum ferritin < 15 ng/mL with HbA2 < 3.5%. The Patra index was calculated as mean corpuscular volume divided by red cell distribution width (MCV/RDW), with a cutoff of ≥5.3 for BTT. RDWI was calculated with a cutoff of <220 for BTT. Diagnostic performance metrics, including sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and 95% confidence intervals (CIs), were determined. Receiver operating characteristic (ROC) curve analysis was performed to assess overall discriminative ability.

Results

Of the 156 patients, 53 (33.97%) had BTT and 103 (66.03%) had IDA. At the predefined cutoff, the Patra index demonstrated a sensitivity of 83.02% (95% CI: 70.2%-91.9%) and a specificity of 100.0% (95% CI: 96.5%-100.0%), yielding a diagnostic accuracy of 94.23%. In comparison, RDWI showed a sensitivity of 100.0% (95% CI: 93.3%-100.0%) and a specificity of 81.55% (95% CI: 72.7%-88.5%), with a diagnostic accuracy of 87.82%. The area under the ROC curve for the Patra index was 0.989.

Conclusion

In this study population, the Patra index exhibited high specificity for differentiating biochemically confirmed BTT from IDA, although its moderate sensitivity limits its utility as a standalone screening tool. It may serve as a simple, cost-effective adjunct or triage tool in resource-limited settings, with confirmatory biochemical testing remaining essential for definitive diagnosis.