Does the mean corpuscular volume help physicians evaluate hospitalized patients with anemia?

The authors analyzed the value of using mean corpuscular volume (MCV) as a guide for selecting tests for further evaluation of anemia in hospitalized patients. Of the 2,082 patients with anemia admitted to the medical service of a teaching hospital over one year, 655 (31%) had further diagnostic tests to evaluate the cause of the anemia. Within this group of 655 patients, 399 (61%) had normal MCVs. Over half the patients with abnormal serum vitamin B12, folate, or ferritin levels, or with low serum iron (Fe) levels with elevated total iron-binding capacity (TIBC), did not have the MCVs expected according to the classification of anemia proposed by Wintrobe. Furthermore, 5% of patients with evidence of iron deficiency had high MCVs, and about 12% of patients with decreased vitamin B12 levels had low MCVs. The MCV was quite specific in identifying patients who had low ferritin levels: specificity was 83%; however, sensitivity was only 48%. The MCV was also specific (88%) for identifying patients who had low Fe with elevated TIBC; however, sensitivity was only 43%. The MCV was poor in identifying patients with abnormalities of serum vitamin B12 and folate levels. In this study the MCV did not provide sufficient diagnostic accuracy to be a useful criterion for the selection of more definitive tests in the evaluation of anemia in hospitalized patients.