Urine Gram Stain as a New Marker in Predicting Postoperative Fever in Patients Undergoing Endourological Surgeries for Stone Disease: A Prospective Study.

INTRODUCTION

Endourological procedures, including ureterorenoscopy (URS), percutaneous nephrolithotomy (PCNL), and retrograde intrarenal surgery (RIRS), are the standard of care for managing urolithiasis but remain associated with postoperative fever (POF). POF is often linked to preoperative bacteriuria or infected stones and can precede urosepsis. While urine culture is the gold standard for detecting urinary tract infections, its 72-hour delay limits perioperative decision-making. Urine Gram stain (UGS) is a rapid and inexpensive diagnostic tool capable of detecting bacteriuria within minutes. This study aimed to evaluate the predictive value of preoperative UGS for POF in patients undergoing endourological surgeries for stone disease.

MATERIALS AND

METHODS

This prospective study enrolled 150 adult patients undergoing URS, PCNL or RIRS for urolithiasis between January 2024 and July 2025. Patients with ongoing sepsis, recent antibiotic use within the preceding 14 days, positive preoperative urine culture, postoperative fever due to other identifiable causes, or incomplete clinical/microbiological data were excluded. Preoperative midstream urine samples were analysed for Gram stain and culture. POF was defined as a temperature ≥38 °C within 72 hours postoperatively, with follow-up extending to capture fevers occurring after discharge during this period. Statistical analysis included chi-square, t-tests, logistic regression, and receiver operating characteristic (ROC) curve analysis to assess the predictive performance of UGS.

RESULTS

POF occurred in 24 patients (16.0%). Positive UGS was observed in 19/24 (79.2%) POF cases versus 21/126 (16.7%) non-POF cases (OR 11.8, 95% CI 4.1-34.2, p<0.0001). Positive urine culture was seen in 16/24 (66.7%) versus 18/126 (14.3%) (OR 5.9, 95% CI 2.1-16.7, p=0.001). UGS demonstrated 79.2% sensitivity, 82.5% specificity, 47.5% positive predictive value, and 94.5% negative predictive value for predicting POF (AUC=0.83, p<0.001). Multivariate analysis confirmed positive UGS (OR 11.8, 95% CI 4.1-34.2) and positive culture (OR 5.9, 95% CI 2.1-16.7) as independent predictors of POF.

CONCLUSION

Preoperative UGS is a rapid, cost-effective, and reliable predictor of POF in endourological stone surgeries. Its integration into preoperative protocols can enhance early risk stratification, enable timely antibiotic optimisation, and potentially reduce postoperative infectious morbidity.