MCV Calculator (Mean Corpuscular Volume)
MCV Calculator (Mean Corpuscular Volume)
Calculate mean corpuscular volume from haematocrit and red cell count, and read the microcytic-normocytic-macrocytic split correctly.
MCV
Red cell sizeHaematocrit 38%, red cell count 4.2 ×10¹²/L
Formula
- Hct
- haematocrit, the packed red cell volume as a percentage of whole blood
- RBC
- red cell count in ×10¹²/L, from the automated cell counter
- × 10
- converts the Hct/RBC ratio into femtolitres per cell
- result
- fL — the mean volume of an individual red cell
Worked example
Haematocrit 38%, red cell count 4.2 ×10¹²/L
38 ÷ 4.2 = 9.0476
9.0476 × 10 = 90.5 fL
MCV categories and common causes
| Category | MCV range | Common causes |
|---|---|---|
| Microcytic | Below 80 fL | Iron deficiency, thalassaemia trait, anaemia of chronic disease, sideroblastic anaemia |
| Normocytic | 80 – 100 fL | Acute blood loss, early iron deficiency, anaemia of chronic disease, mixed deficiency, marrow failure |
| Macrocytic | Above 100 fL | B12 or folate deficiency, alcohol, liver disease, hypothyroidism, myelodysplasia, reticulocytosis, hydroxycarbamide, methotrexate, zidovudine |
What the mean actually hides
MCV is simply the packed red cell volume divided by the red cell count, scaled to femtolitres, and its three-way split into microcytic, normocytic and macrocytic remains the fastest first sort of an anaemia. A microcytic result points toward iron deficiency, thalassaemia trait, anaemia of chronic disease, or — less commonly — sideroblastic anaemia. A macrocytic result raises B12 or folate deficiency with megaloblastic change, alcohol excess, liver disease, hypothyroidism, myelodysplasia, a brisk reticulocytosis, or a drug effect from hydroxycarbamide, methotrexate or zidovudine.
The trap is in the word mean. MCV is an average across every red cell in the sample, and averages hide bimodal populations. A patient with combined iron and B12 deficiency can have a genuinely normal MCV, because a population of small iron-deficient cells and a population of large megaloblastic cells cancel each other out in the arithmetic mean. The automated counter does not miss this entirely — it shows up as a raised red cell distribution width, because RDW measures the spread of cell volumes rather than their average. A normocytic result paired with a high RDW is therefore not reassuring; it is a specific instruction to request a blood film, where the two populations of cells are usually visible on inspection even though the index that summarises them looks unremarkable.
Frequently asked questions
What does a low MCV mean?
Microcytosis, most often from iron deficiency, thalassaemia trait, or anaemia of chronic disease. Sideroblastic anaemia is a less common cause worth considering when the common ones are excluded.
What does a high MCV mean?
Macrocytosis, classically from B12 or folate deficiency with megaloblastic change, but also alcohol, liver disease, hypothyroidism, myelodysplasia, reticulocytosis, or drugs such as hydroxycarbamide, methotrexate and zidovudine.
Can MCV be normal with a mixed deficiency?
Yes. Combined iron and B12 deficiency can average out to a normal MCV because a small-cell population and a large-cell population cancel in the mean. This is why a normocytic result with a raised RDW is worth a blood film.
How is MCV calculated from haematocrit and red cell count?
MCV equals haematocrit divided by red cell count, multiplied by 10 to express the result in femtolitres. Most modern counters measure MCV directly and derive haematocrit from it, but the relationship holds either way.
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References
- Hoffbrand AV, Steensma DP. Hoffbrand’s Essential Haematology. 8th ed.
- Bain BJ. Diagnosis from the blood smear. N Engl J Med. 2005;353(5):498–507.