X-Ray for Kidney Stones: What It Can and Cannot Show

At Independent Physicians Medical Center (IPMC) in Northeast Philadelphia, we offer both X-ray and CT imaging for kidney stone evaluation, helping you and your doctor get answers quickly.

Can an X-Ray Detect Kidney Stones?

A standard abdominal X-ray — often called a KUB (kidneys, ureters, and bladder) X-ray — can detect kidney stones that contain calcium, which fortunately account for about 80 percent of all kidney stones. Calcium-based stones (calcium oxalate and calcium phosphate) are radiopaque, meaning they appear as bright white spots on the X-ray.

However, not all kidney stones are visible on X-ray. Uric acid stones (about 5-10% of kidney stones) are radiolucent, meaning they are invisible on standard X-rays. Cystine stones and some mixed-composition stones may also be difficult to see. Very small calcium stones (under 2 mm) may also be missed.

For this reason, a non-contrast CT scan is considered the gold standard for kidney stone detection, with sensitivity exceeding 95% regardless of stone composition. CT identifies virtually all stones and also shows the exact location, size, and whether the stone is causing obstruction.

When Is a KUB X-Ray Used for Kidney Stones?

Despite its limitations, an X-ray still has a role in kidney stone management:

• Quick initial assessment — X-ray is faster, uses less radiation, and is less expensive than CT, making it a reasonable first step in some clinical scenarios
• Monitoring known stones — once a calcium stone has been identified on CT, follow-up X-rays can track its position and size over time without the higher radiation of repeated CT scans
• Confirming stone passage — after treatment or watchful waiting, X-ray can confirm that a visible stone has moved or passed
• Post-treatment follow-up — checking for residual stone fragments after procedures like lithotripsy (ESWL) or ureteroscopy
• Screening in patients with recurrent calcium stones — periodic X-rays to check for new stone formation

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What to Expect

No preparation is needed. You’ll lie on an X-ray table while a technologist takes an image of your abdomen. The exam takes just a few minutes and is painless. A board-certified radiologist reviews the images and sends a report to your doctor.

If stones are suspected but not visible on X-ray, or if your doctor needs more detailed information about stone size, location, and obstruction, they will recommend a CT scan for a definitive evaluation. At IPMC, both tests are available on-site.