From the Guidelines
The recommended CT scan protocol for diagnosing renal colic is a non-contrast CT scan of the abdomen and pelvis, often referred to as a CT KUB (kidneys, ureters, bladder), with a low-dose protocol to minimize radiation exposure, as supported by the most recent study 1. This protocol involves thin-slice (1-3mm) helical imaging from the top of the kidneys to the base of the bladder without the use of intravenous contrast material. The patient should be positioned supine on the CT table, and the scan should be performed during a single breath hold if possible. The images should be reconstructed in both axial and coronal planes to facilitate stone detection and localization. This non-contrast approach is preferred because it allows for excellent visualization of urinary tract calculi regardless of their composition, as stones appear hyperdense compared to surrounding soft tissues. Additionally, this protocol avoids potential complications associated with contrast administration such as allergic reactions or contrast-induced nephropathy, which is particularly important since patients with renal colic may already have compromised kidney function. In cases where additional information is needed about renal function or anatomy, a delayed contrast phase may be added, but the initial non-contrast scan remains the gold standard for stone detection, as noted in 1 and 1. The use of low-dose CT protocols is also supported by 1, which emphasizes the importance of minimizing radiation exposure while maintaining diagnostic accuracy. Overall, the non-contrast CT KUB with low-dose protocol is the recommended approach for diagnosing renal colic, prioritizing patient safety and diagnostic efficacy.
From the Research
CT Scan Protocol for Diagnosing Renal Colic
The recommended CT scan protocol for diagnosing renal colic involves the use of non-contrast CT scans to minimize radiation exposure while maintaining diagnostic accuracy.
- The use of low-dose non-contrast CT scans with iterative reconstruction techniques, such as adaptive statistical iterative reconstruction (ASiR), can reduce radiation exposure to levels comparable to abdominal radiography 2.
- A study found that reconstructing low-dose CT images with 70% ASiR resulted in superior image quality and diagnostic performance compared to other reconstruction techniques 2.
- The American College of Radiology and other organizations recommend the use of ultrasound or no further imaging in specific clinical scenarios, with reduced-radiation-dose CT to be employed when CT is needed in patients with suspected renal colic 3, 4.
Key Considerations
- The choice of imaging modality depends on the specific clinical scenario and the patient's symptoms and medical history.
- CT scans are accurate but expose patients to ionizing radiation and have not been shown to alter interventional approaches or hospital admission rates 3, 4.
- Ultrasound is a viable alternative to CT scans in some cases, particularly in patients with suspected renal colic who do not require immediate intervention 3, 4.
Diagnostic Performance
- Low-dose CT scans with 70% ASiR have been shown to have a sensitivity and specificity of 87% and 100% for detecting calculi >3 mm 2.
- The diagnostic performance of CT scans can be affected by factors such as stone size, location, and composition, as well as patient factors such as body habitus and renal function.