Two-Step Clinical Rule Improves UTI Diagnosis in Children

Tara Haelle

July 21, 2016

Diagnosing urinary tract infections (UTIs) in young children based on a two-step clinical rule of symptoms and signs yields greater accuracy than a clinical diagnosis on its own, according to a study published in the July/August 2016 issue of the Annals of Family Medicine.

"Our aim was to develop and internally validate a 2-step clinical rule: step 1 used symptoms and signs to select children for urine sampling, and step 2 (once urine was obtained) used symptoms, signs, and dipstick testing to guide empiric antibiotic treatment," explain Alastair D. Hay, MBChB(Sheff), MD(Leic), MRCP, DCH(RCP), MRCGP, DFFP, FHEA, from the University of Bristol in the United Kingdom, and colleagues.

"Based on data obtained from clean-catch samples, we developed novel coefficient (for computer use) and points-based clinical rules to help clinicians select children for urine sampling and antibiotic treatment with high diagnostic utility," the authors conclude. "For step 1, the coefficient-based rule was diagnostically superior to the points-based rule, which in turn was superior to clinical diagnosis," they write. "For step 2, dipstick testing was diagnostically superior to symptoms and signs alone (both coefficient and points-based rules), and was not diagnostically useful in children with the lowest UTI probability, for whom step 1 would not result in urine collection."

Early diagnosis of UTIs in young children is often missed because of insufficient evidence for when a UTI should be suspected, frequently nonspecific symptoms, and the difficulty of collecting a clean urine sample, the authors write. Further, invasive methods using catheterization or suprapubic aspiration risk infection and cause pain and fear.

The researchers therefore enrolled children younger than 5 years who went to one of 233 primary care sites across England and Wales with at least one constitutional symptom and/or at least one urinary tract symptom that are potential markers of UTI. Constitutional symptoms included fever, vomiting, lethargy or malaise, irritability, poor feeding, and failure to thrive. UTI symptoms included "abdominal pain, jaundice in children aged younger than 3 months, hematuria, offensive urine odor, cloudy urine, loin pain, frequency, apparent pain on passing urine, and changes to continence."

After obtaining consent for the study, clinicians recorded results for each child from 107 index tests, which included information obtained from the parent regarding the child's medical history and symptoms, a full clinical exam, and urinary dipstick testing.

Before dipstick testing, clinicians recorded their impression of UTI likelihood (clinical diagnosis).

Clinicians obtained clean catch urine samples from 3036 children, with the assistance of the children's parents. Of those, 2740 (90%) samples had culture results available, nearly all (93.5%) from children aged 2 to 4 years. Just more than half the children were girls.

Overall, 2.2% (n = 60) of the cultured samples were positive according to UK microbiological criteria. However clinicians had diagnosed UTI on the basis of signs and symptoms before urine dipstick testing in 6.1% (n = 168) of the children; just 16.7% (n = 28) of those children were actually positive for a UTI.

Thus, clinical diagnosis had a sensitivity of 46.6% and specificity of 94.7% in this large, population-based sample, with an area under the receiver operator characteristic (AUROC) of 0.77 (95% confidence interval [CI], 071 - 0.83).

The investigators then examined which index test items were significantly associated with a positive urine culture. They found history of a UTI, greater pain or more crying while urinating, urine with an increasingly foul smell, abdominal tenderness during an exam, and the clinician's increasing suspicion of severe illness to be associated with increasing risk of positive culture. In addition, not having a cough and having normal findings from an ear exam were also associated with a culture-confirmed UTI.

Using these signs and symptoms as a clinical rule improved diagnostic accuracy significantly (AUROC, 0.90; 95% CI, 0.85 - 0.95) compared with clinical diagnosis alone.

Adding in the dipstick testing further improved the accuracy (AUROC, 0.93; 95% CI, 0.90 - 0.97).

"[O]ur results support a risk-based approach to the identification of children for investigation of UTI," the authors write.

Although the researchers achieved the highest diagnostic accuracy using a coefficient-based calculation, they note that even using a point system (3 or more of 5 clinical criteria) reduced the number of children who needed urine testing.

The complete details for the rule and cutoff points are available online.

The research was funded by the National Institute for Health Research. The authors have disclosed no relevant financial relationships.

Ann Fam Med. 2016;14:325-336. Full text

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