A low MCV indicates that the red blood cells are microcytic and are smaller than average with a volume of less than 80 femtoliters, according to the American Academy of Family Physicians. The most common cause of a low mean corpuscular volume in the United States is iron deficiency anemia.
Other causes of a low MCV include anemia of chronic disease, lead toxicity, sideroblastic anemia and thalassemia trait, explains the AAFP. The finding of microcytosis alone is not enough to determine the nature of disease and other laboratory exams are necessary. These include serum iron levels, serum ferritin levels, total iron-binding capacity, transferring saturation, red blood cell distribution width, hemoglobin electrophoresis, reticulocyte blood count and peripheral blood smears.
Iron deficiency anemia is a condition that develops when iron stores in the body decrease to a quantity that prevents the normal production of red blood cell, explains Medscape. It is most common in young children, women of child bearing age and pregnant women, notes AAFP. The most common causes include poor iron absorption by digestive system, a diet low in iron, and bleeding, according to Medscape. Symptoms of iron deficiency anemia include fatigue and leg cramps during physical activity, ice cravings, poor academic performance, cold intolerance, reduction in infection resistance, altered behavior, difficulty swallowing and worsening of existing disease.