Urinodling

Urinodling, also called urine culture, is a microbiological test used to detect and identify microorganisms present in urine. It is performed to diagnose urinary tract infections and to assess bacteriuria, the presence of bacteria in urine, in various clinical contexts.

Procedure and interpretation: A urine specimen is collected by clean-catch midstream method or via catheterization, then processed in a clinical microbiology laboratory. The sample is inoculated onto one or more culture media, such as blood agar and MacConkey agar, often using a loop to estimate colony-forming units per milliliter (CFU/mL). Plates are incubated at about 35–37 C for 18–24 hours (longer for some organisms). Growth is assessed by colony number and morphology; organisms are identified using biochemical tests, MALDI-TOF mass spectrometry, or automated systems. Antimicrobial susceptibility testing is performed on isolated pathogens to guide therapy. Results are reported as the identified organism with a colony count and a susceptibility profile.

Significance and limitations: Thresholds for “significant bacteriuria” depend on the clinical context and specimen type. In clean-catch urine from symptomatic patients, counts as low as 10^2–10^3 CFU/mL can be meaningful; traditionally, 10^5 CFU/mL was used as a general cutoff. Catheter-associated infections and men may have different thresholds. False positives can arise from contamination; false negatives may occur after partial treatment or if fastidious organisms are present. Urinodling is complemented by clinical assessment and, when appropriate, urinalysis.

Applications: Diagnosis of urinary tract infections, guiding antibiotic therapy, distinguishing contamination from true bacteriuria, and monitoring bacteriuria in specific patient groups such as pregnant individuals or catheterized patients.