Mean Corpuscular Volume (MCV) is a measure of the average volume, or size, of a single Red Blood Cell. Mean Corpuscular Volume is calculated from the results of Hematocrit test and Red Blood Cell count test. By knowing the size of a Red Blood Cell, it will be possible classify anemia, diagnose its type, and have a better idea of its causes. Depending on the cell size, anemia can be classified into three classes:
- Normocytic Anemia: which includes anemia types that has nothing to do with Red Blood Cell size. Examples include anemia cased by Iron Deficiency or Acute Blood Loss.
- Microcytic Anemia: this class includes types of anemia associated with small size of Red Blood Cells. This class includes anemia caused by Lead Poisoning or Renal Disease.
- Macrocytic Anemia: this class includes types of anemia associated with large Red Blood Cells. Examples include anemia caused Chemotherapy and anemia caused by Vitamin B12 Deficiency.
Mean Corpuscular Volume is one of the Red Blood Cells Indices. To have a better classification of anemia, MCV is used with other RBC Indices (e.g. Mean Corpuscular Hemoglobin). The calculation of Mean Corpuscular Volume is ordered routinely as a part of Complete Blood Cell Count.
MCV is derived by dividing the Hematocrit Level by the total Red Blood Cell Count in a microliter and multiplying the result by 10. The final result will be the average Red Blood Cell size in femtoliters. For example a patient who has a 40% Hematocrit Level and 5 million RBCs/μL his MCV = (40/5) x 10 which equals 80 femtoliter.
Normal values vary according to age and gender. Again, when the MCV value is increased, the RBC is said to be abnormally large, or macrocytic. This is most frequently seen in megaloblastic anemias (e.g., vitamin B12 or folic acid deficiency). When the MCV value is decreased, the RBC is said to be abnormally small, or microcytic. This is associated with iron-deficiency anemia or thalassemia. It is important to recognize that a significant number of patients with disorders associated with a variation in MCV may, in fact, not have an abnormality in MCV. For example, only 65% of patients with iron-deficiency anemia will have a reduced MCV. Furthermore, the normal values for MCV and all of the other RBC indices vary considerably. Each laboratory must develop its own normal index values.
Causes of False Mean Corpuscular Volume Calculation
- Very high White Blood Cell count may cause automated cell counters to calculate wrongfully high Mean Corpuscular Volume.
- High lipid levels (>2000 mg/dL) causes automated cell counters to wrongfully indicate high hemoglobin levels which leads to wrong calculation of high MVC.
- Large Red Blodd Cell precursors cause an abnormally high MCV. Examples of Red Blood Cell precursors include Reticulocytes.
- Drugs that may increase MCV results include azathioprine, phenytoin, and zidovudine.
Normal Mean Corpuscular Volume
Infants are normally born with larger Red Blood Cells than those normally fond in children and adults. The following are the Normal MCV of both groups:
Newborn: 96 to 108 fL.
Child or Adult: 80 to 95 fL.
Causes of Increased Mean Corpuscular Volume
- Pernicious anemia (Vitamin B12 deficiency).
- Folic acid deficiency.
Vitamin B12 deficiency and Folic acid deficiency are the most common causes of macrocytic anemia. These vitamin deficiencies may be caused by malnutrition, malabsorption, competitive parasites, or enzyme deficiencies that impair utilization of these vitamins.
- Antimetabolite therapy: This form of chemotherapy for cancer treatment and, in lesser doses, for arthritis treatment, acts as vitamin B12 and folate inhibitors and can cause a macrocytic anemia.
- Alcoholism: This is probably more related to malnutrition.
- Chronic liver disease: The pathophysiology of this observation is multifactorial and includes poor nutrition, erythropoietin alterations, and the effects of chronic illness.
Causes of Decreased Mean Corpuscular Volume
The most associated diseases with Decreased Mean Corpuscular Volume (Small Red Blood Cells) are:
- Iron-deficiency Anemia.
- Anemia of Chronic Illness.