Clinical utility of routine urine culture before intravesical mitomycin C instillation: A retrospective...

Intravesical mitomycin C (MMC) is widely used after transurethral resection of bladder tumor (TURBT) and as adjuvant therapy for non-muscle-invasive bladder cancer (NMIBC). Despite its favorable safety profile, many institutions continue to require systematic urine culture before each instillation, although supporting evidence is limited.

To evaluate the clinical utility of routine urine culture before intravesical MMC instillation and to assess its association with post-instillation urinary infectious complications.

We conducted a retrospective instillation-based analysis of all intravesical MMC instillations performed at our institution between June 2022 and June 2025. A total of 720 consecutive instillations performed in 78 patients were analyzed. Pre-instillation urine cultures were systematically obtained and classified as negative, polymicrobial, single-organism cultures, or two-organism cultures. The primary outcome was the occurrence of post-instillation urinary infectious complications within 30 days, defined as febrile urinary tract infection, hospitalization for urinary infection, or sepsis, bacteremia.

Among 720 MMC instillations, 639 (88.8%) pre-instillation urine cultures were negative and 81 (11.2%) were non-negative (47 polymicrobial, 26 single-organism cultures, 8 two-organism cultures). Three urinary infectious complications (0.4%) were observed, all occurring in patients with negative pre-instillation urine cultures. No urinary infectious complications occurred in patients with positive urine cultures.

In this retrospective cohort, routine pre-instillation urine culture appeared to have limited clinical utility for predicting subsequent urinary infectious complications. Although these findings support a symptom-based approach in asymptomatic patients, larger prospective studies are needed before definitive recommendations can be made.