From the Guidelines
A non-contrast CT scan of the abdomen is the recommended imaging test for diagnosing kidney stones, as it allows for accurate detection of even small stones with high sensitivity and specificity, as reported in the 2023 study by the Journal of the American College of Radiology 1. The use of non-contrast CT scans for kidney stone detection has several advantages, including:
- High sensitivity and specificity, with a reported sensitivity as high as 97% 1
- Ability to detect stones as small as 1mm
- Ability to determine if stones are causing blockages
- Ability to identify other potential causes of symptoms
- No need for contrast dye, making it safer for patients with kidney problems
- Rapid acquisition with high spatial resolution and ability for multiplanar reformations The radiation exposure from CT scans is a consideration, but it is generally justified by the diagnostic benefits when kidney stones are suspected, and low-dose CT scans have been shown to be effective in detecting kidney stones with a pooled sensitivity of 97% and a pooled specificity of 95% 1. Some key points to consider when using CT scans for kidney stone detection include:
- Stone location and size can be accurately depicted at non-contrast CT and have also been associated with spontaneous stone passage rates 1
- Larger stone size and higher density measured at CT have also been shown to be predictors of the need for invasive management 1
- CT techniques such as use of coronal reformations, viewing on bone window, and use of magnified views can improve the accuracy of stone measurements 1
From the Research
CT Scan for Kidney Stone Diagnosis
- The use of CT scans for diagnosing kidney stones has increased significantly over the years, with a 10-fold increase from 1996 to 2007 2.
- Non-contrast CT scans are becoming the standard imaging modality for urinary stone disease, with low-dose and ultra-low-dose protocols being developed to reduce radiation exposure 3.
- The sensitivity and specificity of ultrasonography (US) for detecting renal calculi are 54% and 91%, respectively, with US significantly overestimating the size of stones in the 0-10 mm range 4.
Stone Detection and Size Determination
- CT scans have a high detection rate for kidney stones, even at low doses, with all types of stones being visible at all settings except for small uric acid fragments 3.
- The size of the stone is an important factor in determining treatment outcomes, with larger stones being more difficult to treat 5, 6.
- Stone density, as measured by CT scans, is also a significant predictor of treatment outcomes, with lower density stones being more likely to be cleared by extracorporeal shock wave lithotripsy (ESWL) 5, 6.
Treatment Outcomes and Predictors
- ESWL is a safe and efficient treatment option for urinary stone disease, with an overall stone-free rate of 63.3% 5.
- Stone size, location, and density are significant predictors of treatment outcomes, with larger stones and those with higher density being more difficult to treat 5, 6.
- The use of non-contrast-enhanced CT scans can provide valuable information for treatment planning, but its advantages over kidney-ureter-bladder film (KUB) are not significant 6.