Design: Systematic review and diagnostic accuracy meta-analysis
Population: 90 studies of children after first or recurrent urinary tract infection
Primary outcome: Accuracy of renal and bladder ultrasound for vesicoureteral reflux
Effect: First UTI: sensitivity 50% (95% CI 42 to 58), specificity 71% (62 to 78); high-grade reflux sensitivity 66%

This systematic review and meta-analysis of 90 studies was carried out to inform the American Academy of Pediatrics' updated guideline on urinary tract infection in young children. It asked how well renal and bladder ultrasound detects vesicoureteral reflux after a first or recurrent UTI.

After a first UTI, pooled sensitivity was 50% (95% CI 42% to 58%) and specificity 71% (62% to 78%). For high-grade reflux (grades III-V), sensitivity rose only to 66%. After recurrent UTI, sensitivity was 26%. The authors rated the evidence low to moderate in certainty and concluded that ultrasound is unreliable as a stand-alone test for reflux.

Ultrasound still has a role in looking for hydronephrosis, structural anomalies and bladder problems after a childhood UTI. What it cannot do is rule reflux in or out. Decisions about micturating cystourethrography should rest on the clinical picture, recurrence and local practice rather than a normal or abnormal scan alone.

Do not use a normal renal and bladder ultrasound to exclude vesicoureteral reflux after a childhood UTI.
Do not use an abnormal ultrasound alone to diagnose reflux; specificity was only about 70%.
Keep ultrasound for detecting hydronephrosis and structural anomalies after a UTI.
Base the decision on micturating cystourethrography on recurrence, clinical features and local guidance.

Why it matters

Ultrasound is often treated as a reflux screen; it misses half of cases after a first infection.

The statistics, in plain English

Sensitivity of 50% means half of children with reflux had a normal-looking ultrasound for reflux. Specificity of 71% means about three in ten without reflux had findings that suggested it. Even for high-grade reflux, a third were missed.