‘Nappy pad’ urine samples for guiding investigation and treatment of urinary tract infection (UTI) in young children: Findings from the ‘DUTY’ prospective diagnostic cohort study

Background
Although sampling urine using nappy pads is preferred by parents and recommended when a clean catch sample can’t be obtained, we do not know the added diagnostic utility of ‘nappy pad’ urine samples, nor the proportion that are contaminated.

Setting
Acutely unwell children <5 years presenting to 233 primary care sites in England and Wales.MethodLogistic regression to identify independent associations of symptoms, signs and urine dipstick test results with UTI; diagnostic utility quantified as area under the receiver operator curves (AUROC). Nappy pad rule characteristics, AUROC, and contamination compared to findings from clean catch samples.

Results
Nappy pad samples were obtained from 3205 children (82% <2 years; 48% female), and culture results available for 2277 (71.0%). 30 (1.3%) met our laboratory definition of UTI. Female gender, smelly urine, darker urine, and absence of nappy rash were independently associated with UTI, with an internally validated, coefficient model AUROC of 0.81 (0.87 for clean catch) that increased to 0.87 (0.90 for clean catch) with the addition of dipstick results. GPs’ ‘working diagnosis’ had an AUROC 0.63 (95% CI 0.53 to 0.72). 12.2% of nappy pad and 1.8% of clean-catch samples were ‘frankly contaminated’ (risk ratio 6.66; 95% CI 4.95 to 8.96; p <0.001).

Conclusion
Nappy pad urine culture results, with features that can be reported by parents and dipstick tests, can be clinically useful, but are less accurate and more often contaminated compared to clean catch urine culture results, which should be prioritised. Dipstick testing adds diagnostic accuracy.