You're reviewing an infant in Paediatric ED with a temperature. They're not too unwell, but the poor parents have been trying to catch a urine sample for 4 hours and everyone's getting a little stressed. If only you could estimate the pre-test probability that the child had a UTI - then you might not even need the sample... And even if you get the sample, how should you interpret it? Just how significant is 1+ leucocytes?

Shaikh N, Hoberman A, Hum S, et al. Development and validation of a calculator for estimating the probability of urinary tract infection in young febrile children. JAMA Pediatr. 2018;172(6):550-556