How this calculator works
Mentzer proposed dividing MCV by the red blood cell count to help distinguish iron deficiency from thalassaemia trait in a microcytic blood count. The original screening boundary is 13: values below it favour thalassaemia trait and values above it favour iron deficiency. Neither pattern proves the cause. Mixed disorders and population differences limit accuracy; iron studies and haemoglobin testing may be needed. Exactly 13 is left indeterminate. The result is an estimate for information only and is not medical advice.
Formula
Mentzer index = MCV (fL) / RBC (millions/µL). The RBC value in x 10^12/L is numerically the same as millions/µL.
Worked example
MCV 70 fL and RBC 5 give index 14. MCV 60 fL and RBC 6 give index 10; these sit on opposite sides of the screening boundary.
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Frequently asked questions
Can I enter RBC as cells/µL?
Convert it to millions/µL first. Enter 5 for a count of 5000000 cells/µL.
Does a value above 13 prove iron deficiency?
No. The index is a screening aid in microcytosis and cannot confirm a diagnosis.
Should I take iron based on this score?
No. Confirm the cause with a clinician; thalassaemia and iron deficiency can coexist.