Analysis of leukopenia and anemia after gastric bypass surgery.

Background: Although anemia is a well-described complication after Roux-en-Y gastric bypass (RYGB) in association with iron deficiency, no studies have been published regarding changes in the white blood cell count.

Methods: Mixed longitudinal models were used to follow the changes in white blood cell count, platelet count, and hematocrit over time after RYGB.

Results: A total of 590 patients, who had undergone RYGB from 2006 to 2010, inclusively, had laboratory studies available. The mean follow-up was 398 days (range 30-1484). The incidence of leukopenia (white blood cell count ≤4000 cm(3)) increased significantly from 2.0% (12 of 590) before surgery to 14.6% (86 of 590) afterward (P < .0005). A lower white blood cell count was independently predicted by greater weight loss, longer time after surgery, a lower hematocrit, and a lower platelet count (P < .0005). No patient developed neutropenia. The incidence of pre-existing anemia was ∼17% for both men and women. After surgery, the incidence of anemia substantially increased only in premenopausal women (from 16% to 33%). Anemia occurred independently of the degree of weight loss. The platelet counts decreased by a clinically insubstantial, although statistically significant, amount (281,000-250,000; P < .0005).

Conclusion: RYGB is associated with a generalized decrease in the white blood cell and platelet counts. These decreases do not seem clinically important, unlike the substantial decrease in red blood cell mass in premenopausal women. A generalized suppression of hematopoiesis might occur after RYGB.