Faculty Bibliography

The sensitivities and specificities of the mean cell volume (MCV), the red cell distribution width (RDW), and blood smear hypersegmentation for B12 deficiency were reviewed in 515 patients whose B12 levels were determined. 61 patients had B12 levels less than 200 pg/ml. 43 patients were defined as B12 deficient (n = 13) or non-B12 deficient (n = 30). Hypersegmentation was more sensitive (91%) than MCV greater than 95 fl (62%) or RDW greater than 15% (54%) in detecting B12 deficiency. The MCV and the RDW should not be relied on when screening for B12 deficiency; examination of the blood smear for hypersegmentation is essential

The usefulness of the red cell distribution width, mean corpuscular volume, and the transferrin saturation in diagnosing iron deficiency anemia were evaluated in a retrospective study of 247 anemic hospitalized patients, many of whom had chronic liver disease. A red cell distribution width greater than 15% had a sensitivity of 71% and a specificity of 54% for iron deficiency as diagnosed by a low serum ferritin or bone marrow examination. A mean corpuscular volume less than 80 femtoliters had a sensitivity of 53% and a specificity of 84%. Transferrin saturation less than 16% had a sensitivity of 61% and a specificity of 86%. Because the sensitivities and specificities of these tests are less than reported in studies of healthier populations, they cannot be relied on for screening for iron deficiency in sick hospitalized patients

Because of recent improvements in the serum vitamin B12 assay, literature criteria based on prior assay methods used in measuring B12 levels were evaluated. Of 1,708 B12 levels measured at Bellevue Hospital in a six-month period, 137 in 124 patients were below 200 pg/ml. Contrary to expectations, 81.6 percent of patients with low B12 levels had a mean corpuscular volume (MCV) below 95 fl. Literature-derived criteria missed 30 percent of patients with low B12 levels. Only three of 12 patients with megaloblastic bone marrow or an abnormal Schilling result had B12 levels that were low (below 100 pg/ml), and nine had values in an intermediate range (100 to 200 pg/ml). This suggests that the use of an MCV below 95 fl and a B12 level below 100 pg/ml as abnormal values may not detect clinically important B12 deficiency