Urinary Tract Infection: 3 Questions Aid Diagnosis in Women

Laurie Barclay, MD

September 09, 2013

Three questions may correctly classify most women with painful and/or frequent urination as having a low or high risk for urinary tract infection (UTI), but others require additional urine dipstick testing, according to a study published in the September/October issue of the Annals of Family Medicine.

"Various medical history questions and urine investigations can be used for UTI diagnosis, of which nitrite, blood, and leukocyte esterase urine dipstick tests, microscopic examination of the urinary sediment, and dipslide are the ones most widely applied," write Bart J. Knottnerus, MD, PhD, from the University of Amsterdam, the Netherlands, and colleagues. "Most of these diagnostic indicators have been studied in single-test evaluations, implying that a test is compared with the urine culture without taking into account the results of preceding tests, including clinical history. In clinical practice, however, the diagnostic work-up is multivariable, and test results are mutually dependent."

The goal of this study was to examine the value of history and urine tests to diagnose uncomplicated UTIs, considering their mutual dependencies and information from preceding tests.

Women with painful and/or frequent urination answered questions about their signs and symptoms and underwent urine tests. The gold standard for diagnosing UTI was 103 colony-forming units/mL on urine culture. The investigators developed a diagnostic index using logistic regression and risk thresholds for UTI of 30% and 70%.

They compared the diagnostic value of 6 models using various combinations of history, dipstick, urinary sediment, and/or dipslide. In the sixth model, only patients with a 30% to 70% risk after the preceding test underwent an additional test.

7 Variables Aid in Diagnosis

Among 196 women studied, prevalence of UTI was 61%. Of 7 variables thought to assist in diagnosis, 3 were from the history, 2 were from dipstick, and 1 each were from sediment and dipslide.

The 3 questions adding most value to the history were "Does the patient think she has a UTI?", "Is there at least considerable pain on urination?", and "Is there vaginal irritation?"

History correctly classified 56% of patients as having a UTI risk of either less than 30% or more than 70%, and adding urine dipstick results increased this correct classification rate to 73%. However, performance was not much better in the 3 models in which urinary sediment and dipslide were added separately and in combination.

Correct classification increased to 83% in the sixth model, in which patients with intermediate risk after history alone underwent an additional test. The strongest indicators of UTI were the patient's suspicion of having a UTI and a positive nitrite test.

"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," the study authors write. "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."

Limitations of this model may include a lack of generalizability to other populations and variability in opinion regarding the cutoff value to be used for defining a urine culture as being positive.

"Our findings imply that UTI diagnosis may be simplified by considerably reducing the number of questions and urine investigations needed," the study authors conclude. "Urinary sediment and dipslide appear to add little information to what is already known from history and dipstick results, implying that performance of these expensive, time-consuming tests might be abandoned."

The study authors have disclosed no relevant financial relationships.

Ann Fam Med. 2013;442-451.

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