From the Guidelines
The gold standard diagnostic test for kidney stones is a non-contrast computed tomography (CT) scan of the abdomen and pelvis. This imaging technique provides detailed visualization of stones in the urinary tract with high sensitivity (95-98%) and specificity (96-98%) 1. A non-contrast CT can detect stones as small as 1mm, identify their exact location, and determine their size and density, which helps predict the likelihood of spontaneous passage. It can also reveal other potential causes of abdominal pain if stones are not present. The scan is relatively quick, taking only a few minutes to complete, and doesn't require the administration of contrast material, making it safer for patients with kidney problems or contrast allergies.
Some of the key benefits of non-contrast CT scans include:
- High sensitivity and specificity for detecting kidney stones 1
- Ability to detect stones as small as 1mm 1
- Can identify the exact location and determine the size and density of the stone 1
- Can reveal other potential causes of abdominal pain if stones are not present 1
- Quick and safe, with no need for contrast material 1
While other imaging methods like ultrasound and X-rays are sometimes used, particularly in pregnant patients or for follow-up examinations to reduce radiation exposure, they don't offer the same level of accuracy as CT scanning for initial diagnosis of kidney stones 1. For example, ultrasound has been found to have a sensitivity of 24% to 57% for stone detection, compared to non-contrast CT 1. Similarly, X-rays have been shown to be 72% sensitive for large stones, but only 29% sensitive overall for the detection of stones of any size in any location 1.
Overall, the evidence suggests that non-contrast CT scans are the most accurate and reliable method for diagnosing kidney stones, and should be used as the first-line diagnostic test in most cases 1.
From the Research
Diagnostic Tests for Kidney Stones
- The gold standard diagnostic test for kidney stones is noncontrast computed tomography (CT) scan 2, 3, 4.
- CT scan is highly sensitive for detecting kidney stones and provides valuable information regarding stone size, composition, location, and overall stone burden 2.
- However, CT scan can be deceiving in some cases, such as when motion artifact causes a warping distortion effect that makes renal stones appear larger than they actually are 2.
- Other diagnostic tests, such as ultrasonography (US), kidney, ureter, and bladder (KUB) plain film radiography, and MRI, have their own advantages and disadvantages 5, 3, 4.
- US is an ideal first-line imaging modality for nephrolithiasis due to its low cost, absence of radiation, and easy availability, but it has reduced sensitivity and specificity compared to CT 3.
- KUB plain film radiography is most helpful in evaluating for interval stone growth in patients with known stone disease, but it is less useful in the setting of acute stones 4.
- MRI provides the possibility of 3D imaging without exposure to radiation, but it is costly and currently stones are difficult to visualize 4.
Sensitivity and Specificity of Diagnostic Tests
- The sensitivity and specificity of US for renal calculi are 45% and 88%, respectively, and for ureteric calculi, they are 45% and 94%, respectively 3.
- The sensitivity of CT scan for detecting renal stones is high, with a sensitivity of 95% for stones ≥3 mm in diameter 5.
- The specificity of CT scan for stone disease on a per-kidney basis is 98% overall, 99% when considering only stones ≥2 mm, and 100% when considering only stones ≥3 mm 5.