From the Guidelines
The best imaging test to diagnose kidney stones is a non-contrast CT scan of the abdomen and pelvis. This test is considered the gold standard for detecting renal stones because it can identify stones of all compositions with approximately 97% sensitivity and specificity, as reported in the most recent study 1. CT scans can visualize stones as small as 1mm, determine their exact location within the urinary tract, and assess for complications like obstruction or infection.
Key Points
- Ultrasound is an alternative option, particularly for pregnant patients or children to avoid radiation exposure, but it's less sensitive than CT, detecting only about 60-80% of stones 1.
- X-ray (KUB) has limited utility as it only detects radiopaque stones, with a sensitivity of 53% to 62% and specificity of 67% to 69% for the detection of ureteral calculi 1.
- While intravenous pyelogram (IVP) was historically used, it has been largely replaced by CT scanning due to CT's superior accuracy, speed, and ability to identify alternative diagnoses that might explain the patient's symptoms.
- For patients requiring repeated imaging or follow-up, low-dose CT protocols can be used to reduce radiation exposure while maintaining diagnostic accuracy, with a pooled sensitivity of 97% and a pooled specificity of 95% 1.
Considerations
- The use of low-dose CT protocols is recommended to reduce radiation exposure, especially in young patients, while maintaining diagnostic accuracy 1.
- MRI may be useful in certain cases, such as detecting and characterizing congenital anomalies of the kidneys and entire genitourinary tract, but it is not the first-line imaging test for diagnosing kidney stones due to its inability to detect smaller calculi 1.
From the Research
Imaging Tests for Renal Stones
The best imaging test to diagnose renal stones is a topic of discussion among medical professionals. Several studies have investigated the accuracy and effectiveness of different imaging modalities in detecting renal stones.
- Non-contrast spiral computerized tomography (CT) is considered one of the most accurate methods for detecting renal stones, with a detection rate of up to 95% 2.
- Ultrasonography (US) is also a commonly used imaging modality for detecting renal stones, with a sensitivity of 81% and specificity of 100% for renal stones, but its sensitivity for ureteric stones is lower, at 46% 3.
- Plain X-ray of the kidney, ureter, and bladder (KUB) regions is another imaging modality used to detect renal stones, but its sensitivity is lower compared to CT and US 4.
- Low-dose non-contrast CT with adaptive statistical iterative reconstruction (ASiR) has been shown to have high sensitivity and specificity for detecting calculi >3 mm, with a sensitivity of 87% and specificity of 100% 5.
- Non-contrast enhanced multi-slice CT-KUB is also an effective imaging modality for detecting renal stones, with a high sensitivity and specificity, and can identify alternate causes of pain other than stones 6.
Comparison of Imaging Modalities
The choice of imaging modality depends on various factors, including the patient's symptoms, medical history, and the availability of imaging equipment.
- CT scans are generally more sensitive and specific than US and plain X-ray, but they involve higher radiation exposure.
- US is a non-invasive and relatively low-cost imaging modality, but its sensitivity for ureteric stones is lower compared to CT.
- Plain X-ray is a simple and widely available imaging modality, but its sensitivity is lower compared to CT and US.
Key Findings
- Non-contrast CT is the most accurate imaging modality for detecting renal stones, with a detection rate of up to 95% 2.
- Low-dose non-contrast CT with ASiR can detect calculi >3 mm with high sensitivity and specificity 5.
- Non-contrast enhanced multi-slice CT-KUB is an effective imaging modality for detecting renal stones and identifying alternate causes of pain 6.