Predictors of Pyelonephritis in Patients with Urolithiasis: A Retrospective Case-Control Study

Pyelonephritis is quite common in patients with urolithiasis. This condition not only complicates the management of urolithiasis but also makes the treatment of associated urinary tract infections more challenging. The aim of this study is to identify the risk factors for pyelonephritis in patients with urolithiasis.

A total of 8,273 patients with urolithiasis were retrospectively screened (2016-2025). From this cohort, 302 patients who developed pyelonephritis and 302 age- and gender-matched controls without pyelonephritis were randomly selected, forming a matched case-control study population. Demographic and clinical variables, including age, gender, stone size and location, number of stones, comorbidities, prior urinary operation, presence of a double-J ureteral stent, and urinary tract obstruction, were analyzed as potential risk factors.

Pyelonephritis developed in 302 patients (53.3% female). Hydronephrosis was the strongest independent risk factor, increasing risk nearly ninefold. Other significant risk factors included hypertension, diabetes mellitus, chronic kidney disease, malignant disease, immunosuppression, larger stone burden, multiple and bilateral stones, ureteral stent presence, and prior urinary operation. Each 1-mm increase in stone size was associated with a 2.3% increase in the risk of developing pyelonephritis. Bacteremia was detected in 66 patients, and urine cultures were positive in 229 patients. Escherichia coli was the most common pathogen, followed by Klebsiella pneumoniae and Pseudomonas aeruginosa.

Hydronephrosis, ureteral stent presence, a history of open or laparoscopic intervention, hypertension, and higher stone burden were independently associated with the development of pyelonephritis in patients with urolithiasis. Gram-negative bacilli were the most frequently isolated pathogens. Identification of these risk factors may support earlier recognition of high-risk patients and guide preventive and therapeutic decision-making. Prospective multi-center studies are needed to confirm these findings.