Lab Test: MCV, Mean Corpuscular Volume Level
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- Provides information about the size of red blood cells (RBCs).
- Useful in classifying anemias.
- This test is routinely performed as part of an automated complete blood cell count. The results, along with other test results, are necessary to calculate the RBC indices. When investigating anemia, it is helpful to categorize the anemia according to the RBC indices. Cell size is indicated by the terms "normocytic", "microcytic", and "macrocytic".
- The MCV is a measure of the average volume, or size, of a single RBC, and is therefore used in classifying anemias. MCV is derived by dividing the hematocrit by the total RBC count:
- MCV = Hematocrit (%) X 10 รท RBC (million/mm3).
- Normal values vary according to age and gender. 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.
- Increased levels may indicate:
- Pernicious anemia (vitamin B12 deficiency), folic acid deficiency, antimetabolite therapy, alcoholism, or chronic liver disease
- Decreased
levels may indicate:
- Iron-deficiency anemia, thalassemia, anemia of chronic illness
- Hematocrit - this is a measurement of the percentage of the total blood volume taken up by the RBCs. It is closely associated with the RBC count.
- Hemoglobin - this is a measurement of the concentration of hemoglobin in the blood ad is closely associated with the RBC count.
- Extremely elevated WBC counts (>50,000) may increase the MCV when processed by automated counters.
- Large RBC precursors, for example, reticulocytes, cause an abnormally high MCV. This commonly occurs in response to anemias when the bone marrow is not pathologic.
- Marked elevations in lipid levels (>2000 mg/dL) causes automated cell counters to indicate high hemoglobin levels. MCV will be calculated falsely high.
- The presence of cold agglutinins also falsely elevates MCV.
- Drugs that may increase MCV results include: azathioprine, phenytoin, and zidovudine.
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Collect a venous blood sample.
- Avoid hemolysis.
- Apply pressure or a pressure dressing to the venipuncture site and assess the site for bleeding.
- Transport the specimen to the hematology laboratory, in which the blood is passed through automated machines that calculate the RBC indices.
Indications & Uses
Clinical Application
Related Tests
Drug-Lab Interactions
Procedure
Storage and Handling
MESH Terms & Keywords
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