system
Medical AI Inquiry: You were designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.
user
What is the most likely diagnosis if a urine sample collected for routine testing darkens on standing?
assistant
The correct answer is  Urine turns dark on standing in alkaptonuria due to the formation of black coloured alkaptone bodies. Ref: Textbook of Biochemistry By DM Vasudevan, 3rd Edition, Page 184 ; Harper's Biochemistry, 25th Edition, Page 332