Weight-Independent Percentile Chart of 2880 Gastric Bypass Patients: a New Look at Bariatric Weight Loss Results.

BACKGROUND: Percentile charts would be ideal for assessing sufficient weight loss in bariatric surgery. They allow comparing individual results to the outcome of many others, at any postoperative time. Unfortunately, percentile charts can be problematic when comparing unequally heavy peers, a circumstance not uncommon among bariatric patients. We investigate the relevance of this disadvantage and combine new insights to improve the practical use of percentile charts in bariatric surgery. METHODS: Laparoscopic Roux-en-Y gastric bypass outcome expressed with body mass index (BMI), excess weight loss (%EWL), total weight loss (%TWL), and alterable weight loss (%AWL), a new metric rendering outcome independent of baseline BMI, is used to build percentile curves p97/p90/p75/p50/p25/p10/p03 with the lambda-mu-sigma method. We used the %AWL p25 curve as baseline BMI-independent reference for sufficient weight loss and compared it to p25 curves based on common metrics and to traditional criteria ≥50 % EWL, <25 % EWL, and BMI < 35 kg/m2. RESULTS: We operated 2880 patients, with baseline BMI of 43.4 kg/m2, follow-up 71 %, and mean of 23.3 (0-87.6) months. Independent %AWL outcome is presented in one percentile chart. Percentile curves p25/p50/p75 show 40/48/57 % AWL at nadir 15/16/19 months, 35/45/54 % AWL at 3 years, and 30/38/47 % AWL at 7 years. Traditional criteria and p25 curves based on %EWL and BMI match with most sufficient results (high sensitivities), but overlook many insufficient results (low specificities). CONCLUSIONS: We present the first baseline BMI-independent bariatric weight loss percentile chart. It allows comparing heavier patients to lighter peers and vice versa, at any postoperative time, up to 7 years. With these advantages, we compared it to traditional bariatric criteria like ≥50 % EWL and found that they are weak in recognizing insufficient weight loss. The visual aspect of consecutive results plotted on a chart among the percentile curves of peers conveys a strong, intuitive message on the personal progress of postoperative weight loss.