What is your approach to patients with suspected renal stones? Scan them all? Scan the first-timers? Scan the older patients? It's certainly easy to order a noncontrast CT scan, even directly from triage.
But what about ultrasound? It has been somewhat of a forgotten test for evaluating renal colic, perhaps in part because it relies upon secondary findings of renal stones, namely hydronephrosis and the absence of ureteral jets, because ureteral stones are not easily visualized with ultrasound. But perhaps it's time to re-evaluate, given the cost and radiation involved with multiple CT scans.
A landmark multicenter study in 2014 compared noncontrast CT, radiology-performed ultrasound, and point-of-care ultrasound in evaluating patients with suspected renal colic. (New Engl J Med 2014;371:1100.) This well-powered, prospective trial found no significant difference in diagnostic accuracy. The rate of significant adverse events was not found to be significantly different. The length of ED stay, however, was found to be significantly shorter in patients receiving only point-of-care ultrasound, although the lengths of stay for those in the CT and radiology-performed ultrasound groups were similar.
The New England Journal of Medicine study may convince you that ultrasound deserves a place at the renal stone table, but it doesn't answer every question. If I suspect my patient has a renal stone, for example, how can I assess the size of the stone and more importantly, the likelihood that it will pass on its own?
The STONE score (sex, timing, origin, nausea, erythrocytes) was developed and validated as a means to determine which patient characteristics make a diagnosis of renal stones more likely. (BMJ 2014;348:g2191.) The higher the score, the more likely the patient's symptoms are caused by renal colic. The lower the score, the more likely an alternative diagnosis is to blame. A white man with acute onset of pain associated with nausea and vomiting and found to have hematuria has a high score and, therefore, a high likelihood of renal stone as the etiology of his symptoms.
STONE PLUS is a clinical prediction tool recently proposed to integrate point-of-care ultrasound, specifically the finding of hydronephrosis, into the assessment of patients with suspected renal colic. (Ann Emerg Med 2016;67:439.) The authors of this study found that the presence of hydronephrosis on point-of-care ultrasound substantially increased the sensitivity (67% to 98%) and specificity (57% to 74%) in the low and moderate STONE score groups. They also found that the presence of hydronephrosis increased the likelihood of future urologic intervention. Interestingly, their study correlated the amount of hydronephrosis with the size of the stone, something that has not been well demonstrated before.
What to make of all this? Think about using ultrasound, either at the bedside or radiology-performed, to evaluate patients with suspected renal stones. It is as accurate as CT in making the diagnosis and finding hydronephrosis, and can help predict which patients are likely to require further intervention.
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