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Thomas Fanshawe's latest blog discusses a study of over 1000 women to evaluate the effectiveness of UTI diagnostic guidelines in primary care. It underlines the potential for misdiagnosis and calls for improved point-of-care tests.

Abstract image of bladder and medical testing

Urinary tract infection (UTI) is the most common bacterial infection among women attending primary care, with half of all women experiencing at least one UTI in their lifetime. However, quick diagnosis can be challenging, because symptoms can be similar to those caused by other conditions. UTI is a distressing condition, causing pain and limiting the daily functioning of those affected, and may lead to complications including bloodstream infections if not treated promptly.

Accurate early diagnosis of UTI is important as it allows suitable treatment, usually antibiotics, to be prescribed appropriately, while avoiding unnecessary prescriptions being given to those who will not benefit from them. As a result, current guidelines in England (UKHSA, formerly Public Health England, guideline GW-1263, and Scotland (Scottish Intercollegiate Guidelines Network guideline SIGN160, provide diagnostic flowcharts to support UTI diagnosis and antibiotic prescribing in primary care.

These flowcharts use information about the patient’s symptoms, such as pain when urinating and frequency of urination, together with results from a urine dipstick that can be performed in a GP surgery, to assess the likelihood of a UTI. There is little published evidence to support their performance in a real-world primary care environment.

We used data from more than 1000 women attending primary care with symptoms of suspected UTI to assess the performance of these guidelines. We compare the diagnostic recommendation for each woman, as derived from the flowcharts, with the result of a laboratory urine culture. A positive urine culture is the current best practice for confirming a diagnosis of UTI, but does not help GPs decide whether to prescribe antibiotics because results take several days to be available.

Urine culture results of study participants (right-hand axis) in comparison of risk category derived from the GW-1263 diagnostic guideline (left-hand axis). (click to expand)Urine culture results of study participants (right-hand axis) in comparison of risk category derived from the GW-1263 diagnostic guideline (left-hand axis). (click to expand)The UKHSA guideline classifies women into three risk groups, labelled ‘UTI likely’, ‘UTI equally likely’ and ‘UTI less likely’. We found that 61% (311/509) of women classified as ‘UTI likely’ had a positive urine culture, with 13% (64/509) having a negative urine culture and the remainder being mixed growth, meaning that a UTI could neither be confirmed nor ruled out. However, even in the group of women classified as ‘UTI less likely’, where antibiotics were not advised, 40% (80/199) had a positive urine culture, with only 29% (58/199) having a negative urine culture (see Figure).

For the SIGN guideline, the highest risk group, where antibiotics would be recommended had a high chance of a positive urine culture (73%, 60/82), with only 2% (2/82) having negative culture, but this guideline performed less well in detecting the lower risk categories, with more than 40% of participants having a positive urine culture in these groups, where clinicians would be advised not to prescribe antibiotics.

Our study quantifies the performance of current guidelines for the first time. Although we think the guidelines have some diagnostic capability, we think it is important for GPs to recognise that they have the potential for significant levels of misdiagnosis, and do not always identify the individuals who are most likely to benefit from an antibiotic prescription. Infection among symptomatic patients cannot usually be confidently excluded, based on the guidelines. We recommend that clinicians should robustly safety net women who are not prescribed antibiotics regarding the need to re-present and the possible complications of UTI.

Given the non-specific nature of many of the symptoms, there is likely to be a ceiling on the level of diagnostic accuracy that can be achieved using symptom information and dipstick results alone. For these reasons, a research priority should be to investigate the performance of point-of-care tests for UTI which can be used at the time of first consultation.

The paper was published in the Journal of Antimicrobial Chemotherapy and is available here:

The views expressed here are those of the authors and not necessarily those of the NIHR, the NHS or the Department of Health and Social Care. Readers' comments will be moderated - see our guidelines for further information.