BMI-stratified nomograms to predict early SIRS-defined sepsis after flexible ureteroscopy

Postoperative sepsis is a serious complication of flexible ureteroscopy (FURS). Body mass index (BMI) may modify risk, but BMI-stratified prediction models are lacking. We developed and internally validated BMI-specific nomograms for early SIRS-defined sepsis after FURS.

This single-center retrospective cohort included 1,254 adults undergoing FURS (2020-2024), stratified by BMI (<25 vs. ≥ 25 kg/m²). Multivariable logistic regression identified independent predictors of SIRS-defined sepsis within 48 h in each stratum. BMI-specific nomograms were constructed and internally validated using 1,000 bootstrap resamples.

SIRS-defined sepsis occurred in 78/1,254 (6.2%): 42/504 (8.3%) with BMI ≥ 25 vs. 36/750 (4.8%) with BMI < 25 (p = 0.011). In both strata, positive urine culture, staghorn stones, CRP ≥ 10 mg/L, and procalcitonin ≥0.5 ng/mL were independent risk factors. Operative time ≥60 min was significant only in the BMI ≥ 25 group, while postoperative albumin ≥35 g/L was protective only in the BMI < 25 group. The BMI ≥ 25 nomogram showed excellent discrimination (AUC 0.94, optimism-corrected 0.92), and the BMI < 25 nomogram performed robustly (AUC 0.90, optimism-corrected 0.88), with good calibration and net benefit.

BMI-stratified nomograms identified shared and BMI-specific risk factors for early SIRS-defined sepsis after FURS. These tools may aid individualized perioperative risk assessment, pending external validation.