Ultrasonography: Everyone <6 months, and recurrent infections (see below) in children >6 months.
Urgent ultrasonography (at time of the infection): < 3 yrs with atypical infection (see below) or <6 months with with recurrent infection (see below).
Atypical infection – any of the following:
No response to 48 hrs appropriate antibiotic treatment
Poor urine flow
Non-E. Coli organism
Raised serum creatinine
Recurrent infection: 3 or more episodes of LUTI, or 2 episodes UTI if either of them was an upper UTI.
Micturating cystography – gold standard (if done by a skilled radiologist) but invasive (requires catheterisation) and involves ionising radiation (equivalent to about 4/12 background radiation). Indications: <6/12 with atypical infection or recurrent infection. Consider if abnormal ultrasound.
DMSA – < 3 years with atypical or recurrent UTIs. (Looks for scarring.)
(BMJ 2013; 346: e8654 doi: 10.1136/bmj.e8654)