Can X-ray Show Kidney Stones?
Yes, plain X-ray (KUB) can show kidney stones, but only detects approximately 53-68% of stones and should not be used as a standalone test for diagnosing kidney stones. 1
Why X-ray Has Limited Utility
Approximately 90% of kidney stones are radiopaque (composed of calcium oxalate, calcium phosphate, or struvite), meaning they theoretically should be visible on X-ray, but actual detection rates are much lower in clinical practice 1
Plain radiography (KUB) has limited sensitivity of 53-62% and specificity of 67-69% for detecting ureteral calculi, making it an unreliable standalone test 1
X-ray is particularly insensitive for stones <4 mm and those located in the mid and distal ureters, where overlying bowel gas and bone structures obscure visualization 1
X-ray cannot detect radiolucent stones (uric acid stones, which comprise 12% of all kidney stones), making it miss a significant proportion of cases 2
When X-ray Can Be Useful
Adding KUB to ultrasound improves stone detection from 24-57% (ultrasound alone) to 79-90% sensitivity when CT is not appropriate 1
In patients with known hydronephrosis on ultrasound, adding KUB increased sensitivity from 39% to 68% for large stones and from 60% to 82% for stones requiring intervention 1
If a stone is visible on the CT planning image (scout film), it will be 100% visible on a formal KUB radiograph, though the converse is not true—many KUB-visible stones are not seen on CT scout films 3
The Gold Standard Alternative
Non-contrast CT of the abdomen and pelvis is the reference standard with 97% sensitivity and 95% specificity, and should be the first-line imaging test for suspected kidney stones 1, 4, 5
Virtually all renal calculi are radiopaque on CT, allowing accurate detection of even small stones without IV contrast 1, 4
Low-dose CT protocols (<3 mSv) maintain 97% sensitivity and 95% specificity while minimizing radiation exposure, addressing concerns about cumulative radiation in stone formers 1, 5
Clinical Bottom Line
Do not rely on plain X-ray alone to diagnose or exclude kidney stones. If CT is contraindicated (pregnancy, children), use ultrasound combined with KUB rather than either modality alone 1, 5. For all other patients, proceed directly to low-dose non-contrast CT as the definitive diagnostic test 4, 5.