## Distinguishing Calcium Oxalate from Uric Acid Stones ### Radiographic Appearance **Key Point:** Calcium oxalate stones are radiopaque (visible on plain X-ray) due to their calcium content, whereas uric acid stones are radiolucent (not visible on plain radiography). ### Comparative Features | Feature | Calcium Oxalate | Uric Acid | |---------|-----------------|----------| | **Radiopacity** | Radiopaque (visible on KUB) | Radiolucent (not visible on KUB) | | **Urine pH** | Acidic to neutral (pH 5.5–7.0) | Acidic urine (pH < 5.5) | | **Prevalence** | Most common (70–75% of stones) | 5–10% of stones | | **Risk factors** | Hypercalciuria, hyperoxaluria | Gout, high purine diet, dehydration | | **Imaging modality** | Visible on plain X-ray, CT, ultrasound | Requires CT (non-contrast CT is gold standard) | | **Treatment** | Thiazide diuretics, citrate supplementation | Allopurinol, urate-lowering therapy | ### Clinical Pearl **High-Yield:** The **radiopacity of calcium oxalate stones on plain radiography** is the single best discriminating feature. A radiolucent stone on KUB in a patient with recurrent nephrolithiasis should raise suspicion for uric acid stone, mandating CT imaging for confirmation and serum uric acid assessment. ### Why This Matters **Tip:** On NEET PG, when a question presents a radiolucent stone on plain film in a patient with nephrolithiasis, think uric acid stone first. Conversely, a radiopaque stone on KUB is almost always calcium oxalate (or calcium phosphate). [cite:Campbell-Walsh Urology 12e Ch 52]
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.