A CT Scan KUB (Kidneys, Ureters, Bladder - Plain) is a specialized non-contrast (plain) computed tomography scan that images the urinary tract—from the kidneys, down the ureters, to the bladder. It is commonly referred to online as CT KUB, kidney stone CT, renal calculus scan, or urolithiasis scan.

This test uses X-rays and computer processing to create detailed cross-sectional images. Because it is done without contrast dye, it is especially good at detecting calcifications, including most types of kidney and ureteric stones. Many centers use a low-dose protocol to reduce radiation while still providing images optimized to find stones and assess obstruction.

What it looks for / measures:

• Kidney, ureter, or bladder stones (their size, number, and exact location)
• Urinary obstruction (for example, swelling of the kidney/ureter upstream from a blocked stone)
• Hydronephrosis and hydroureter (dilation caused by blockage)
• Other causes of flank or lower abdominal pain that may mimic stones (sometimes visible even on a plain CT)

In plain language, what results often mean:

• “Stone seen”: A calcified stone is present. The report will usually note size (mm) and location (kidney vs ureter). Smaller stones are more likely to pass on their own; larger stones may need medication or procedures.
• “Obstruction / hydronephrosis”: Urine flow may be blocked, often by a stone. This can require urgent assessment—especially if there is fever, infection, worsening pain, or reduced kidney function.
• “No stone detected”: A stone is less likely, but symptoms could be from other conditions (or occasionally a very tiny stone or non-calcified cause). Your clinician correlates the scan with symptoms and urine tests.
• “Incidental findings”: A plain CT KUB may reveal unrelated findings in nearby organs. These are common and may or may not need follow-up.

A CT KUB is most often ordered when a clinician suspects a kidney stone (renal calculus) or a stone in the ureter causing renal colic. It is valued because it is fast, highly sensitive for most stones, and helps guide treatment decisions (watchful waiting vs medical therapy vs intervention).

Typical symptoms that prompt a CT KUB include:

• Sudden, severe flank pain (side/back pain) that may come in waves
• Pain that radiates to the lower abdomen or groin
• Blood in urine (pink, red, or tea-colored urine) or microscopic hematuria on a urine test
• Nausea and vomiting associated with severe pain
• Painful urination, frequent urge to urinate, or difficulty passing urine
• Concern for urinary blockage, especially with decreased urine output

Why doctors choose a plain (non-contrast) CT KUB:

• It is one of the best imaging tests for urolithiasis and ureteric stones.
• No IV contrast is needed, which can be helpful for people with contrast allergy or certain kidney issues where contrast is avoided.
• It can show secondary signs of obstruction (like hydronephrosis) that influence urgency and management.

Risk factors that may increase suspicion of stones and lead to ordering a kidney stone CT include a prior history of stones, dehydration/low fluid intake, diets high in salt or animal protein, recurrent urinary infections, gout or high uric acid, certain metabolic conditions (e.g., hyperparathyroidism), obesity, and a family history of stones.

Important notes: CT involves radiation. Many facilities use low-dose CT KUB, but your clinician may consider ultrasound or other imaging in certain groups (such as pregnancy) depending on symptoms and clinical urgency.

• Kidney stones (nephrolithiasis / renal calculi)
• Ureteric stones (ureterolithiasis)
• Bladder stones (vesical calculi)
• Urolithiasis (stones anywhere in the urinary tract)
• Obstructive uropathy (urinary tract blockage)
• Hydronephrosis / hydroureter due to obstruction
• Recurrent renal colic
• Urinary tract infection complicated by suspected obstruction (to evaluate for an obstructing stone)

• Identifying the cause of severe flank pain quickly to support timely treatment decisions
• Confirming or ruling out a suspected kidney or ureter stone (CT KUB / kidney stone CT)
• Assessing stone size and location to help plan passing strategies, medications, or procedures
• Checking for urinary blockage and protecting kidney function by detecting hydronephrosis early
• Guiding prevention strategies for recurrent stones (by documenting stone burden and recurrence)
• Evaluating persistent blood in urine when stones are suspected as a cause
• Supporting follow-up after a stone episode to confirm resolution when clinically indicated