Urinary tract infection in adults — KFP-style written assessment

KFP 1 (10 marks)

A 26-year-old woman presents with 48 hours of dysuria, frequency and suprapubic pain. No fever, no loin pain. She reports no vaginal discharge or irritation. A nurse has already done a dipstick: leukocyte esterase positive, nitrite negative. ^[1]

1. What is her pre-test probability of UTI on symptoms alone, and how does the symptom combination change it? (4) ^[1]
2. The nitrite-negative result worries the nurse. Interpret it. (3) ^[1]
3. Should you send urine culture before treating? Justify. (3) ^[5]

Model answers

1. Any urinary symptom carries roughly a 50% pre-test probability of UTI. Dysuria plus frequency WITHOUT vaginal discharge or irritation raises the probability above 90% — enough to rule in the diagnosis on history alone and treat empirically. ^[1]
2. Nitrite negativity does not lower probability usefully: history, examination and dipstick together cannot reliably reduce post-test probability to a level where UTI is excluded once urinary symptoms exist. Frequent voiding can also produce false-negative nitrites. Treat the story, not the stick. ^[1]
3. No — culture is for when results change management: men, pregnancy, recurrence, failure, pyelonephritis or diagnostic doubt. Uncomplicated cystitis with a classic history needs empiric narrow-spectrum therapy only. ^[5]