Thirty-day outcomes after bariatric conversion operations: a national analysis of 94,828 cases

Conversion bariatric operations are increasing and now comprise nearly 10% of procedures nationally, yet their 30-day risk compared with primary operations remains poorly characterized at the pathway level.

To estimate the adjusted excess 30-day serious adverse event (SAE) risk of conversion versus primary bariatric operations of the same final anatomy, and to identify which pathways carry the highest risk.

National Metabolic and Bariatric Surgery Accreditation and Quality Improvement Program (MBSAQIP) Participant Use File (PUF), 2020 to 2024.

We performed anatomy-stratified logistic regression with marginal standardization on 949,507 bariatric operations (94,828 conversions). The primary outcome was a 17-component composite SAE. Adjusted risk differences (RDs) per 1000 were computed for sleeve gastrectomy (SG), Roux-en-Y gastric bypass (RYGB), and biliopancreatic diversion with duodenal switch (DS)/single-anastomosis duodeno-ileal (SADI) strata, and a within-conversion model identified associated factors.

Conversion was associated with higher adjusted 30-day SAE risk across all anatomies: SG (RD 18.2 per 1000 [95% confidence interval, CI: 15.0-21.3], number needed to harm [NNH] 55), RYGB (22.1 [19.5-24.7], NNH 45), and DS/SADI (17.5 [9.4-25.7], NNH 57). The excess was concentrated in utilization events (reoperation, reintervention, and readmission) and selected technical complications, such as leak, organ-space infection, and bowel obstruction. Among conversions, a prior RYGB carried the highest risk (adjusted odds ratio [aOR]: 2.54 versus a prior sleeve). The excess showed no detectable change across study years.

Conversion operations carry a clinically meaningful excess 30-day SAE risk that is greatest after a prior gastric bypass. Conversion status should be treated as a distinct risk category rather than benchmarked against primary procedures alone.