Is computed tomography (CT) with or without contrast indicated for diagnosing kidney stones (nephrolithiasis)?

From the Guidelines

For kidney stone evaluation, a non-contrast CT scan is the preferred imaging method. Non-contrast CT scans provide excellent visualization of kidney stones without requiring the administration of contrast material, with a reported sensitivity as high as 97% 1. This approach is considered the gold standard for kidney stone detection and can accurately identify the size, number, and location of stones. Non-contrast CT also allows assessment of stone density (measured in Hounsfield units), which can help predict stone composition and guide treatment decisions.

Key Points

• Non-contrast CT scans have a high sensitivity for detecting kidney stones, exceeding 95% 1
• Contrast-enhanced CT is generally unnecessary for routine kidney stone evaluation and may actually obscure small stones as the contrast can have similar density to the stones themselves
• Using non-contrast CT avoids potential complications associated with contrast agents such as allergic reactions and contrast-induced nephropathy, which is particularly important since patients with kidney stones may already have compromised renal function 1
• The non-contrast approach also makes the study quicker, less expensive, and more accessible
• If there is suspicion of other pathology beyond simple urolithiasis, such as complicated infection, abscess, or tumor, a contrast-enhanced study might be warranted as a secondary investigation 1

Considerations

• Low-dose non-contrast CT regimens should be used to minimize radiation exposure, especially in young patients 1
• The sensitivity for stone detection decreases with smaller stone size, and low-dose CT may have a lower sensitivity for small stones 1
• Stone location and size can be accurately depicted at non-contrast CT and have been associated with spontaneous stone passage rates, with more proximal as well as larger stones having a higher need for intervention 1

From the Research

CT Scan for Kidney Stones

• Non-contrast CT scan (NCCT) is becoming the standard imaging modality in urinary stone disease 2
• Low-dose and ultra-low-dose protocols exist for NCCT, and studies have shown that ultra-low-dose CT has a good detection rate for all kinds of stones, even when the fragment size is small 2
• The use of contrast-enhanced CT is not typically necessary for detecting renal stones, as NCCT is sufficient for diagnosis 3

Detection Rate of Renal Stones

• The detection rate of renal stones on contrast-enhanced CT is extremely high for stones ≥ 6 mm 3
• The detection rate for stones measuring 3-5 mm is 82-88% on contrast-enhanced CT 3
• NCCT has a high detection rate for all kinds of stones, with the exception of small uric acid fragments, which may require higher energy settings to be detected 2

Imaging Protocols

• A novel protocol, including oral hydration and an oral diuretic, has been shown to increase the distention of the renal collecting system on NCCT, allowing for better preoperative planning for stone removal 4
• The use of a diuresis enhanced non-contrast computed tomography for kidney stones protocol (DRINK protocol) has been shown to increase the visible collecting system volume and surface area, and expand the upper and lower pole infundibular widths and the width of the renal pelvis 4

Trends in Imaging Utilization

• The utilization of CT scans for suspected urolithiasis has increased significantly over the past few decades, from 4.0% to 42.5% between 1996 and 2007 5
• The use of ultrasound (US) for suspected urolithiasis has remained low, at around 5%, and has actually decreased in recent years 5