Abdominal CT is the most common initial imaging test ordered for suspected nephrolithiasis in the Emergency Department. This is largely due to its high sensitivity for the diagnosis of kidney stones and ability to assess for other high-risk diagnosis. However, CT scan results in exposure to ionizing radiation with related long-term cancer risk and a high rate of incidental findings. CT scanning leads to increased ED length of stay and also contributes to the growing annual care cost of acute nephrolithiasis. Emergency Physician performed ultrasound (Point-of-Care (POC) US) is a safe and efficient alternative to CT for evaluation of acute nephrolithiasis in the Emergency Department. No evidence to date has shown that increased CT use improves clinical outcomes.
In patients presenting with renal colic, is an ultrasound first approach equivalent to a CT first diagnostic strategy?
Patients age 18-76 years of age presenting to the ED with suspected nephrolithiasis.
POC US or Radiologist performed US
• High-risk diagnoses with complications that could be related to missed or delayed diagnosis
• Cumulative radiation exposure from imaging
• Total Cost (not reported)—ongoing project
• Return to the ED and hospitalizations after discharge
• Serious adverse events
• Pain (rated on 11 point visual analogue scale)
• Diagnostic accuracy for nephrolithiasis (compared baseline dx at time of discharge from the ED with reference standard of confirmed stone dx: patients observation of passage of stone or by patients report that stone was removed)
Multi-center randomized comparative effectiveness trial
• Patients in whom the treating physician considered to be at high risk for an alternative diagnosis
• Pregnant women
• Obesity (men >285, women >250 lbs)
• Patients with a single kidney, renal transplant patients, dialysis patients
- No significant difference in serious adverse events across groups
- Diagnostic accuracy of imaging was similar in 3 study groups (35% in POC US, 31% in radiological us group, 32% in CT group)
- High-risk diagnoses with complications during the first 30 days were recorded in 11 patients (0.4%) with no statistically significant difference according to study group (P=0.30).
- Average cumulative radiation exposures were lower in patients assigned to point-of-care ultrasonography and radiology ultrasonography than in those assigned to CT (10.1 mSv and 9.3 mSv, respectively, vs. 17.2 mSv; P<0.001). This difference was attributed to the imaging performed at the baseline emergency department visit by the authors.
- Large, multicenter trial
- Study asked a clear clinical question that was patient centered
- Minimal exclusions increasing applicability
- Some patients lost to follow up
- Cannot apply to obese population or pregnant women
Patients in the US group were more likely than those in the CT group to undergo additional diagnostic testing during the initial ED visit. However, despite the additional imaging tests ordered for the patients assigned to ultrasound, the mean total cost for the ED visit were lower and mean radiation exposure in the ultrasound groups was about half that in the CT group.
“Initial ultrasonography was associated with lower cumulative radiation exposure than initial CT, without significant differences in high-risk diagnoses with complications, serious adverse events, pain scores, return emergency department visits, or hospitalizations.”
If you suspect nephrolithiasis, start with bedside ultrasound. If you see hydronephrosis, you've made your diagnosis and you can rest easy regarding the relative incidence of missed alternative diagnoses at least based on the findings in this study. By applying this approach in the Emergency Department you can potentially lower cumulative radiation exposure in patients with suspected nephrolithiasis.
Potential Impact To Current Practice
Application of an ultrasound first approach in patients with suspected nephrolithiasis can lower cumulative radiation exposure by decreasing CT usage.
Ultrasound should be considered as the initial diagnostic imaging test for suspected nephrolithiasis in the ED.
- ALiEM: Author Insight: Ultrasonography versus CT for suspected nephrolithiasis | NEJM
- EM Literature of Note: Farewell, CT Stone Protocol
- EM Ireland: RCT of ED Renal Ultrasound for Renal Colic
- SGEM#97: Hippy Hippy Shake – Ultrasound Vs. CT Scan for Diagnosing Renal Colic