Diagnostic studies-urinary tract infections

(NEJM 2016;374:562)

• Urinalysis: pyuria + bacteriuria ± hematuria ± nitrites

• Urine Cx (clean-catch midstream or straight-cath) Obtain cx only if symptoms (although in ill Pts, can include ∆MS, autonomic instability) ⊕ if: ≥105 CFU/mL, though <105 but ≥102/mL may still indicate UTI in some scenarios Pyuria & ⊖ UCx=sterile pyuria. Ddx: prior abx, nephrolithiasis, interstitial nephritis, tumor, TB, urethritis (see “STI”)

• Catheter-associated: requires (1) s/s (incl atypical) + (2) urine Cx w/ 1 species ≥103 colonies from clean urine sample (after replacing Foley). Pyuria alone not sufficient to dx

• Blood cultures: obtain in febrile Pts; consider in complicated UTIs

• For all men w/ UTI, consider prostatitis: ✓ prostate exam

• CT A/P: consider in severely ill, obstruction, persistent sx after 48–72 hours of approp abx

More detailed

• Perform a urinalysis to check for pyuria and bacteriuria, and check for additional symptoms such as hematuria and nitrites.
• Obtain a urine culture (clean-catch midstream or straight-cath) only if there are symptoms present, although in ill patients, symptoms may include changes in mental status or autonomic instability. A positive culture is considered ≥105 CFU/mL, but a count of ≥102/mL may still indicate a UTI in some cases. If there is pyuria present but the urine culture is negative, it is referred to as sterile pyuria. Consider differential diagnoses such as prior antibiotic use, nephrolithiasis, interstitial nephritis, tumor, tuberculosis, and urethritis.
• For catheter-associated UTIs, both symptoms (including atypical symptoms) and a urine culture with a count of at least 103 colonies from a clean urine sample (after replacing the catheter) are required for diagnosis. Pyuria alone is not sufficient for a diagnosis.
• Obtain blood cultures in febrile patients and consider obtaining them in complicated UTIs.
• For all men with UTIs, consider the possibility of prostatitis and perform a prostate exam.
• Consider a CT scan of the abdomen and pelvis in severely ill patients, in cases of obstruction, or in cases of persistent symptoms after 48-72 hours of appropriate antibiotic treatment.