A simple ratio from your CBC that helps suggest iron lack versus inherited thalassemia as causes of small red cells.
The Mentzer index is a calculated value, not a separate blood test. It uses two figures from a full blood count, the mean corpuscular volume (MCV) and the red blood cell count (RBC), to help distinguish two common causes of small red cells.
The formula is: Mentzer index = MCV ÷ RBC count (in millions per microlitre).
Both iron deficiency anaemia and beta thalassaemia trait produce small red blood cells, but they differ in how many cells the body makes. The Mentzer index uses that difference to point toward one cause or the other.
A value above 13 suggests iron deficiency anaemia, where the body makes fewer, smaller cells. A value below 13 suggests thalassaemia trait, where many small cells are produced. It is a screening clue, not a diagnosis.
Aniva reads your result against research-backed ranges, not just the lab's wide normal. The reference shown below is specific to this biomarker.
Interpretive thresholds:
The index is a screening guide only and needs confirmation with iron studies and haemoglobin electrophoresis.
The index can be misleading when iron deficiency and thalassaemia coexist, or in mixed anaemias. It depends on accurate red cell indices, which automated analysers usually provide reliably, but it cannot replace confirmatory testing.
Read with its components, MCV and red blood cell count, and alongside ferritin, iron studies and haemoglobin electrophoresis.
What does a high or low Mentzer Index mean? Higher values tend to fit iron lack, while lower values may fit thalassemia trait. It’s a clue, not a diagnosis.
Do I need to fast for this test? No. The index uses your CBC values, and fasting does not meaningfully change it.
What can affect results? Iron pills, transfusion, illness, dehydration, pregnancy, altitude, and heavy exercise can shift MCV or RBC count and the ratio.
How often should I test it? As advised by your clinician. It’s usually repeated with CBC when checking response to treatment or clarifying microcytosis.
How long do results take? Results are usually ready in about 7 days.
What should I discuss with my clinician? Ask about next steps such as ferritin, iron studies, or hemoglobin electrophoresis, and whether diet, bleeding, or family history could be relevant.
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