Toward a simple diagnostic index for acute uncomplicated urinary tract infections.

PURPOSE: Whereas a diagnosis of acute uncomplicated urinary tract infection (UTI) in clinical practice comprises a battery of several diagnostic tests, these tests are often studied separately (in isolation from other test results). We wanted to determine the value of history and urine tests for diagnosis of uncomplicated UTIs, taking into account their mutual dependencies and information from preceding tests.

METHODS: Women with painful and/or frequent micturition answered questions about their signs and symptoms (history) of UTIs and underwent urine tests. A culture was the reference standard (10(3) colony-forming units per milliliter). A diagnostic index was derived using logistic regression with bootstrapped backward selection and parameter-wise shrinkage. Risk thresholds for UTI of 30% and 70% were used to analyze discriminative properties. Six models were compared: (1) history only, (2) history+ urine dipstick, (3) history+ urine dipstick + urinary sediment, (4) history+ urine dipstick+ dipslide, and (5) history+ urine dipstick+ urinary sediment+ dipslide; we then added (6) a test only for patients with an intermediate risk (between 30% and 70%) after the preceding test.

RESULTS: One hundred ninety-six women were included (UTI prevalence 61%). Seven variables were selected from history (3), dipstick (2), sediment (1), and dipslide (1). History correctly classified 56% of patients as having a UTI risk of either <30% or >70%. History and urine dipstick raised this to 73%. The 3 models with the addition of urinary sediment and dipslide, separately and in combination, performed hardly better. The sixth model, in which those at intermediate risk after history and received an additional test, correctly classified 83%. The patient's suspicion of a UTI and a positive nitrite test were the strongest indicators of a UTI.

CONCLUSIONS: Most women with painful and/or frequent micturition can be correctly classified as having either a low or a high risk of UTI by asking 3 questions: Does the patient think she has a UTI? Is there at least considerable pain on micturition? Is there vaginal irritation? Other women require additional urine dipstick investigation. Sediment and dipslide have little added value. External validation of these recommendations is required before they are implemented in practice.