question and answer
What's behind isolated high MCV?
March 2003
"What's the significance of an increased mean corpuscular volume (MCV) of 105 fL in a woman with normal hemoglobin and B[subscript 12]/folate levels?" queries A. SORENSEN, MD, of OSHAWA, ON, adding, "She's not taking any medication, and testing was done for poor energy and fatigue. Her thyroid- stimulating hormone (TSH) was also normal."
Several conditions show normal serum folate and B[subscript 12] but high MCV, including: *chronic alcoholism; *liver disease; *obstructive jaundice; *marrow suppression or infiltration; *myelodysplasia; *hypothyroidism; *high reticulocyte count of any cause. In North America, the most frequent cause is chronic alcoholism. Another common condition is falsely elevated MCV due to the presence of cold agglutinin. In the presence of cold agglutinin, red cells stick together at room temperature, so the instrument that determines the complete blood count (CBC) would underestimate the red cell count and overestimate the MCV and mean corpuscular hemoglobin concentration (MCHC). Finding that both MCHC and MCV are high should alert an experienced laboratory technologist to check for the presence of cold agglutinin or red cell agglutination on blood smear. MS
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