Calculators & Tools

Mentzer Index

Thalassaemia trait versus iron deficiency in microcytosis

1 What is the Mentzer Index?

The Mentzer index divides the mean corpuscular volume by the red cell count to help separate beta-thalassaemia trait from iron deficiency in a child with microcytic anaemia. It is a screening aid, useful in settings where both conditions are common.

2 When to use it

  • A child with microcytic anaemia on a routine full blood count
  • Deciding whether to pursue haemoglobin electrophoresis or iron studies first
  • Population screening where thalassaemia trait is prevalent

3 Formula & method

The index is MCV divided by the red blood cell count. Thalassaemia trait typically produces a relatively preserved or raised red cell count with a low MCV, giving a low index; iron deficiency reduces the red cell count alongside the MCV, giving a higher index. The app states which pattern the entered values suggest.
  • Mentzer WC. Differentiation of iron deficiency from thalassaemia trait. Lancet. 1973

4 Frequently asked questions

Is the Mentzer index diagnostic?

No. It is a discrimination aid that suggests which line of investigation to pursue. Confirmation needs iron studies or haemoglobin electrophoresis and HbA2.

Can a child have both conditions?

Yes, and coexisting iron deficiency and thalassaemia trait is common in India. Combined disease blunts the index and can make it misleading.

Does it work in young infants?

It is less reliable in the first months of life, when red cell indices are changing physiologically.

Are there other discrimination indices?

Several exist, including the Green & King and Srivastava indices. None is reliable enough to replace confirmatory testing.

For qualified clinicians. This page and the PediAid app are a clinical aid only. Calculations and reference data must be verified against the patient's clinical context, the source guideline and your local protocols before any treatment decision is made.