Hematologic complications of gastric bypass for morbid obesity.

Of 530 patients who have had a gastric bypass operation for morbid obesity at Allegheny General Hospital, 41 had decreases in serum iron, vitamin B12, and/or folate levels. These abnormalities were detected eight months to eight years (median, two years) after the operation. The hemoglobin level ranged from 7.4 to 14.1 gm/dl at the time of detection, and mean corpuscular volume (MCV) ranged from 58 to 119 cu microns. The most common problem was combined iron and vitamin B12 deficiencies. Physicians should be aware that folate, vitamin B12, and iron deficiencies occur after gastric bypass, though the time to development is variable. Hemoglobin level and MCV are not predictive of these deficiencies.