This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Anatomy
A lady presents with right knee swelling.Aspiration was done in which CPPD crystals were obtained.Next best investigation is 
Select and explain. 
A. ANA, B. RF, C. CPK, D. TSH
D: TSH
Answer: D: TSH 
Explanation: Secondary CPPD deposition is associated with hypothyroid,hence TSH level should be assessed. Other conditions: Hyperparathyroidism Hemochromatosis Hypophosphaemia Hypomagnesemia Diabetes