Background

Anemia is a common nutritional complication after bariatric surgery, with a reported incidence of 20-50%. To date, no model has been established to identify patients at high risk of postoperative anemia to guide nutritional monitoring and supplementation. We aimed to develop a nomogram for predicting anemia 1 year after bariatric surgery.

Methods

Patients with obesity undergoing bariatric surgery in China-Japan Friendship Hospital between 2018 and 2020 were reviewed. Anemia is defined according to the WHO criteria. Predictors were identified using univariate and multivariate logistic regression analyses to establish the nomogram. The discriminative ability, calibration, and clinical value of the nomogram were tested using the area under the curve (AUC), calibration plot, and decision curve analysis. The nomogram was internally validated using 1000 bootstrap resampling.

Results

A total of 281 patients were enrolled, and 108 (38.4%) patients experienced anemia 1 year after surgery. According to multivariate analyses and clinical significance, gender, age, surgical type, preoperative anemia status, preoperative ferritin, folate, and VitB12 levels were risk factors for postoperative anemia and incorporated to develop the nomogram. The nomogram showed good discrimination, with the bootstrap bias-corrected AUC of 0.790 (0.732-0.838). The brier score (0.181) and calibration plot both indicated excellent calibration. Under the Youden index of 0.374, sensitivity was 76.9%, specificity was 72.8%, and accuracy was 74.4%. Decision curve analysis further confirmed the clinical usefulness of the nomogram.

Conclusions

The first nomogram for predicting anemia after bariatric surgery had an excellent predictive value, which may help guide postoperative nutritional monitoring and supplementation.