Laparoscopic sleeve gastrectomy (LSG) and the Roux-en Y gastric bypass (RYGB) are currently the most commonly performed weight loss surgery (WLS) procedures. Studies comparing the risk of anemia between these two procedures are lacking.


We reviewed the electronic medical records of 3346 patients who had undergone WLS from 2004-2017 in a racially-mixed population at Boston Medical Center. Hemoglobin (Hb) trajectories were characterized by mixed linear model analyses. Anemia was defined by Hb concentration below 12.0 in women and below 13.0 in men. Presence or absence of anemia was evaluated at each patient visit. Cox regression analysis (proportional hazards ratio, HR) and generalized equation estimator model (Odds ratio, OR) were used to compare the risks of time-to-event and repeated events, respectively.


Significant factors affecting the occurrence of anemia were sex (female), age, surgery type and race. Hb deceased similarly in the in the first year after LSG and RYGB (p<0.0001); time-to-event HR was not significant for RYGB relative to LSG. However, one year after surgery, Hb increased to baseline in LSG but not in RYGB (P<0.0001 for surgery x time interaction). OR for persistent anemia was significantly higher in RYGB (1.62, p<0.0001, relative to LSG).Compared to other racial groups, African Americans (AA) had significantly higher HR (3.94, p=0.002) and OR (2.35, p<0.0001) for time-to event and persistent anemia, respectively.


Anemia prevalence is similar between LSG and RYGB in the first year but is more likely to persist after the RYGB. AA are at higher risk for acute and chronic anemia after WLS compared to other racial groups. Further studies should assess adherence to postoperative vitamin/mineral supplementation and prescribed iron repletion.