We tend to think of iron deficiency anemia (IDA) as being microcytic (more consistently than hypochromic). However, there are certain situations in which the mean cell volume (MCV) is normal in IDA.
Examples include:
- A patient with high-normal baseline MCV whose MCV falls within the normal range in IDA.
- A patient with baseline macrocytosis, for example from concomitant liver disease, vitamin B12 deficiency, myelodysplastic syndrome (MDS) or hydroxyurea use.
- Rare cases where the MCV simply doesn’t budge from baseline despite clear cut evidence of IDA (i.e. anemia +/- low mean corpuscular hemoglobin concentration [MCHC] with low ferritin that responds to iron treatment).
Consider the case in the graphic below. This is a 36 yo pregnant female with IDA, but MCV and MCHC within the normal range. Note however, that her MCV of 85 at the peak of her IDA, while in the normal range, is low for her (5 fL below baseline).
Studies have demonstrated a mean increase in MCV of about 5 fL during pregnancy (physiological macrocytosis of pregnancy). So, if she were not pregnant, IDA may have led to an MCV < 85 fL.
Note the telltale increase in RDW (anisocytosis) following treatment with IV iron. Finally, note the physiological leukocytosis of pregnancy.
