US vs. CT for Kidney Stones
Dr. Adam Webb
Kidney stones are not uncommon in the ED, and with the explosion of CT scanners we often scan patients looking specifically for stones. However, this exposes a lot of patients to perhaps unnecessary radiation.
I picked this article because I had a patient who was too large for our CT scanner, and I was interested in how accurate and reliable other imaging modalities are in the diagnosis of nephrolithiasis. While this study did not directly answer my question, as obese patients were excluded, it did shed light on the role ultrasonography can play in diagnosing kidney stones in the ED.
Ultrasonography versus Computed Tomography for Suspected Nephrolithiasis
N Engl J Med 2014; 371:1100-1110
This was a multicenter, pragmatic, comparative effectiveness trial. Patients were randomly assigned to ultrasonography performed by ED physicians, or by radiology, or abdominal CT scan. Primary endpoint was 30-day incidence of high-risk diagnoses with complications that could be related to missed or delayed diagnosis and the 6-month cumulative radiation exposure. Secondary outcomes were serious adverse events, pain, return to the ED, hospitalizations, and diagnostic accuracy.
Sensitivity and specificity for CT in this study was 86% and 53%, which are much lower than most reported rates in the rest of the literature. This is likely because the standard for diagnosis (passing a stone, or having surgery) was so high.
Ultrasound has a place as an imaging modality for kidney stones.
Starting with US for high suspicion of kidney stone as the primary diagnosis is not unreasonable.