What red cell indices are
A complete blood count (CBC) reports hemoglobin, hematocrit and the red blood cell count. From them, three red cell indices describe the average size and hemoglobin content of red cells. They are the first step in working out the cause of anemia.
The formulas
- MCV (mean corpuscular volume, fL) = hematocrit (%) × 10 ÷ RBC (million/µL)
- MCH (mean corpuscular hemoglobin, pg) = hemoglobin (g/dL) × 10 ÷ RBC
- MCHC (mean corpuscular hemoglobin concentration, g/dL) = hemoglobin × 100 ÷ hematocrit
- Mentzer index = MCV ÷ RBC
Worked example
Hemoglobin 11 g/dL, hematocrit 34%, RBC 5.0 million/µL:
- MCV = 34 × 10 ÷ 5.0 = 68 fL: microcytic
- MCH = 11 × 10 ÷ 5.0 = 22 pg: hypochromic
- MCHC = 11 × 100 ÷ 34 = 32.4 g/dL: low normal
- Mentzer = 68 ÷ 5.0 = 13.6: slightly favors iron deficiency over thalassemia trait
Reference ranges (adults)
| Index | Typical range |
|---|---|
| MCV | 80–100 fL |
| MCH | 27–33 pg |
| MCHC | 32–36 g/dL |
Classifying anemia by MCV
| Type | MCV | Common causes |
|---|---|---|
| Microcytic | below 80 | Iron deficiency, thalassemia trait, anemia of chronic disease, lead poisoning |
| Normocytic | 80–100 | Blood loss, kidney disease, chronic inflammation, early iron deficiency, hemolysis |
| Macrocytic | above 100 | Vitamin B12 or folate deficiency, alcohol, liver disease, hypothyroidism, some medicines |
The Mentzer index
In a microcytic anemia, iron deficiency produces fewer, smaller cells, while thalassemia trait produces many very small cells with a relatively normal or high red cell count. A Mentzer index below 13 suggests thalassemia trait; above 13 suggests iron deficiency. It is a screening clue only: ferritin, iron studies and hemoglobin electrophoresis confirm the diagnosis, and the two conditions can coexist.
Other useful values
- RDW (red cell distribution width) is often high in iron deficiency and normal in thalassemia trait.
- The reticulocyte count shows whether the bone marrow is responding to the anemia.
- Modern analyzers measure MCV directly and calculate hematocrit, so small differences from the hand calculation are normal.
This calculator is for general information and education. It is not medical advice and does not replace the judgment of a doctor, nurse or pharmacist who knows the full clinical picture.