Mentzer Index

The Mentzer Index is a simple bedside tool for distinguishing two common causes of microcytic anaemia: iron deficiency vs thalassaemia trait. It only appears on your report when mean red-cell volume is low (MCV < 80 fL), because outside microcytosis the ratio is not clinically informative.

A low ratio (< 13) suggests thalassaemia trait — the body makes many small red cells, a benign genetic variant. A high ratio (≥ 13) suggests iron deficiency anaemia — the body makes fewer, proportionally small red cells because iron stores are depleted.

Shortness of breath on exertion, fatigue, pale skin, cold extremities, brittle nails, restless legs. Thalassaemia trait is typically asymptomatic.

For iron-deficiency pattern: red meat, liver, shellfish, legumes paired with vitamin-C sources. For thalassaemia trait no dietary change is indicated — avoid iron supplementation unless serum iron studies confirm deficiency.

For iron-deficiency pattern: tea and coffee with meals (block iron absorption), excessive calcium supplementation at mealtimes.