POCUS for Kidney Stone – Be Careful

July 3, 2018

Written by Clay Smith

Spoon Feed
Point-of-care ultrasound (POCUS) in patients with renal colic had tepid diagnostic accuracy for nephrolithiasis.  If hydronephrosis was present, specificity was 94% and often indicated a stone >5mm.

Why does this matter?
Normal bedside ultrasound does not rule out nephrolithiasis.  It is important to understand the diagnostic accuracy of the tests we use every day in practice.  This is one example.

Stones are hard
This was a meta-analysis of 5 studies with use of POCUS for nephrolithiasis in the ED for patients with renal colic.  They found the overall sensitivity of POCUS was 70%, specificity 75%.  That’s not so great.  In two of the studies, presence of moderate to severe hydronephrosis had 94% specificity for stone.  What this tells us is that bedside POCUS isn’t that accurate in diagnosing nephrolithiasis, but that is not new information. POCUS is helpful when hydronephrosis is present, as there is probably a stone >5mm.  Whether this is managed with subsequent CT or expectant medical management depends on the clinical scenario.

Source
The Accuracy and Prognostic Value of Point-of-care Ultrasound for Nephrolithiasis in the Emergency Department: A Systematic Review and Meta-analysis.  Acad Emerg Med. 2018 Jun;25(6):684-698. doi: 10.1111/acem.13388. Epub 2018 Mar 25.
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Reviewed by Thomas Davis

Another Spoonful
Don’t miss ALiEM’s Top 10 Reasons Not to Order a CT for Renal Colic.