Question

Which kidney stone is radiolucent on a plain KUB X-ray?

• A. \(Calcium\ oxalate\ stone\)
• B. \(Struvite\ stone\)
• C. \(Uric\ acid\ stone\)
• D. \(Calcium\ phosphate\ stone\)

Hint:

The "I Can't See U" mnemonic: "I" for invisible, "U" for Uric acid. Most stones are radiopaque; Uric acid, Crixivan (Indinavir), and Xanthine stones are the primary radiolucent ones.

Answer 1

The Correct Option is C

Step 1: Recall stone composition.
Most urinary stones like calcium oxalate, calcium phosphate and struvite contain calcium or heavy metals, which block X-rays
Step 2: Identify the exception.
Uric acid stones are made of a pure organic compound with no calcium, so they do not absorb X-rays the same way
Step 3: Conclude the finding.
On a plain KUB film a uric acid stone appears radiolucent, showing up only as a filling defect rather than a bright spot
\[ \boxed{Uric acid stone} \]