A 13-year-old boy presents with jaundice, fatigue, muscle stiffness, tremors, behavioral changes, hepatosplenomegaly, and Kayser-Fleischer rings. Which test is definitive for the diagnosis?

Options

1. Urinary copper
2. Serum ceruloplasmin
3. Hepatic parenchymal copper concentration
4. Genetic testing for ATP7B mutation

Correct Answer

Serum ceruloplasmin

Explanation

The clinical presentation is consistent with Wilson disease, a disorder of copper metabolism. Serum ceruloplasmin is typically decreased (<20 mg/dL) and is the most commonly used definitive diagnostic test. Kayser-Fleischer rings are pathognomonic for Wilson disease.

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