Written by Clay Smith
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.
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
Don’t miss ALiEM’s Top 10 Reasons Not to Order a CT for Renal Colic.
3 thoughts on “POCUS for Kidney Stone – Be Careful”
Great paper. Ultrasound can be very useful for initial evaluation of suspected renal colic especially with recurrent kidney stones. Safe according to Binder study but always need to consider other diagnosis. Be careful with their conclusion “any hydro suggests a stone greater than 5mm.” Probably better to think about no-mild hydro ~15% chance of stone greater than 5 mm with almost no chance of stone greater than 10mm and moderate to severe hydro ~35% chance of stone greater than 5 mm (Goertz 2010). I think saying that any hydro means they probably have a stone > 5 mm may be misleading and would not be accurate to provide this information to the patient. As with any meta analysis, especially POCUS data where studies are quite varied in terms of experience of operator, inclusion/exclusion criteria and methods, I encourage reviewing each study individually to have a better understanding about how the numbers apply to you.
Important study/outcome to know, though I dont think we should use/are using POCUS as our definitive diagnostic tool. I think we are using it to determine if there is significant hydonephrosis/ureter and therefore a stone we may be more likley to need to intervene on.
True. An ultrasound first approach is safe and reduced overall CT use. http://pmid.us/25229916