Because mean corpuscular volume, or MCV, measures the size of a patient's red blood cells, or RBCs, a low MCV number indicates smaller-than-normal RBCs. Small RBCs indicate a condition known as microcytic anemia, which has numerous causes, the most common being iron-deficient anemia.
The MCV number is a standard measurements taken as part of a complete blood count, or CBC test. It specifically measures the average size and volume of a person's RBCs, using the range of 78 to 98 fL as the benchmark for "normal" in adults, 78 to 120 fL for children ages 12 to 18, 70 to 86 fL for children ages 6 months to 2 years and 95 to 121 fL for newborns up to 6 months of age.
A low MCV reading, defined as anything under 80 fL in adults, means that RBCs are abnormally small because of either a failure of hemoglobin to synthesize RBCs or a lack of available hemoglobin to complete the task. The leading cause for this condition in both children and adults is iron-deficiency anemia whereby the iron stores in the blood are low due to blood loss, insufficient dietary intake or iron, absorption problems or other factors. Iron plays an important role in the production of RBCs, and iron-deficiency anemia is one of the most common causes of anemia cases worldwide.