Which Factors Are Associated with a Higher Prevalence of Anemia Following Bariatric Surgery? Results from a Retrospective Study Involving 1999 Patients.

Introduction: Anemia in obese patients is common and multifactorial and is also a complication of bariatric surgery. The aim of this study is to establish which variables are associated with a higher prevalence of post-bariatric surgery anemia.
Methods: Retrospective cohort study involving 1999 patients submitted to bariatric surgery with a follow-up period of 4 years. Anthropometric, laboratorial parameters and the presence of comorbidities were evaluated before surgery and during follow-up. Patients were divided into two groups, according to whether they developed anemia, or not. Groups were compared using independent sample T-tests or Chi-squared tests, as appropriate. Univariate binary logistic regression models were used to test the association between the diagnosis of anemia during follow-up and all the possible explanatory variables. Independent variables with an association with the outcome (p < 0.1) were included in multivariate binary logistic regression models, as well as possible confounders (age, BMI, and supplementation).
Results: Anemia was diagnosed in 24.4% of the patients. Females present a two-fold increased risk of developing anemia (OR 2.11, 95% CI 1.48-3.01, p < 0.001). Patients subjected to gastric sleeve and gastric band surgery present approximately half the risk of anemia when compared with gastric bypass surgery (RYGB) (OR 0.46, 95% CI 0.35-0.59, p < 0.001; OR 0.51, 95% CI 0.36-0.72, p < 0.001). None of the other variables evaluated showed association with the outcome.
Conclusion: In our study, the only factors associated with an increased risk of developing anemia were female gender and RYBG surgery. Prospective studies evaluating the risk factors for anemia in patients undergoing bariatric surgery are needed.