Dr Abdul Mannan FRCPath FCPS
Blood 🩸Doctor
A structured, evidence-based review of the Mentzer Index for differentiating iron deficiency anaemia from β-thalassaemia trait in microcytic anaemia.
The Mentzer Index (MI) is calculated from routine full blood count parameters:
MI = MCV (fL) / RBC count (×10¹²/L)
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Interpretation
Originally described by Mentzer (Lancet, 1973) as a simple screening tool for microcytic anaemia differentiation.
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The index exploits fundamental haematological differences:
| Parameter | Iron Deficiency Anaemia | β-Thalassaemia Trait |
|---|---|---|
| RBC count | ↓↓ (reduced production) | Normal or ↑ (ineffective erythropoiesis) |
| MCV | ↓↓ (small cells) | ↓↓ (small cells) |
| Mentzer Index | High (>13) | Low (<13) |
| Mechanism | Fewer small cells | Many small cells |
Performance varies significantly across studies and populations:
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Key Performance Metrics
Sensitivity for βTT: 60–99% (highly variable)
Specificity for βTT: 60–95%
NPV for βTT: Often >95% (excellent rule-out)
PPV for βTT: Variable (8–80%, depends on prevalence)
No single index achieves 100% sensitivity and specificity across all populations.
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| Study | Population | Sensitivity (βTT) | Specificity (βTT) | Comments |
|---|---|---|---|---|
| Vehapoglu 2014 | Turkish children | 98.7% | 82.3% | Best single index in this cohort |
| Ntaios et al. (2007, Ann Hematol) | Greek adults ( 493 ) | 84.8 % | 89% | Green & King outperformed Mentzer |
| Saudi 2023 | 434 children | 74% | 63% | High IDA prevalence; PPV only 8% |
| Pakistan Antenatal MI Diagnostic Study (NMU, 2019) | Pregnant women | 83% | 91% | Resource-limited setting |
| Sherali (Pakistan) | Children 1–5y | 80.7% | 77.7% | Moderate performance |
Clinical Implication: Performance is context-dependent – influenced by population prevalence, age, ethnicity, and severity of anaemia.