Weight loss reporting: predicted body mass index after bariatric surgery

BMI and %EBMIL are the most accurate methods for comparing results of patients after bariatric surgery. %EBMIL is based on BMI 25 as a constant end-point for all patients, but BMI 25 is easily achieved by patients with BMI < 50, whereas it is not so feasible for patients with BMI > 50. We were prompted to obtain by statistical methods a mathematical formula able to calculate the final BMI (FBMI) 3 years after the operation, dependent on the initial or preoperative BMI (IBMI) of a multicenter group of morbid obese patients operated with different bariatric techniques. We also obtained a specific formula for each bariatric procedure of this group of patients. We propose the name Predicted BMI for the value obtained with these formulas and its application in the %EBMIL instead of the constant value of BMI 25. We have analyzed the IBMI and FBMI of a multicenter group of 7,410 patients, subjected to different bariatric procedures with a minimum follow-up of 36 months. Statistical methods with a linear regression model have been used to obtain the two types (global and specific) of Predicted BMI. We first obtained a general formula of PBMI = IBMI x 0.4 + 11.75 for the total population of patients, and a second specific formula for each bariatric technique: PBMI = IBMI x 0.43 + 13.25 + technique_correction_adjustment. Predicted BMI and its application to the %EBMIL may result in a more rational comparison of results of bariatric patients, bariatric techniques, and groups of bariatric surgeons. Predicted BMI may advance the BMI that each patient would probably achieve after surgery.