This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Inborn Errors of Metabolism, Subject name: Pediatrics
Ferric chloride test is used to diagnose: 
Select and explain. 
A. Phenylketonuria, B. Alkaptonuria, C. Hartnup disease, D. Cystinuria
A: Phenylketonuria
Answer: A: Phenylketonuria 
Explanation: a. Pheylketonuria(Ref: Nelson's 20/e p 636-642; Ghai 8/e p 653-655)Ferric chloride test is used to determine the presence or absence of phenols in a given sample.FeCl3 test with urine gives green colour in Phenylketonuria (detects phenylalanine in urine).