A lady presents with right knee swelling. Aspiration was done in which CPPD crystals were obtained. Next best investigation is :

TSH Finding CPPD crystal in aspirated synol fluid is diagnostic of CPPD ahropathy. CPPD ahropathy in some patients may be associated with : - Primary hyperparathyroidism - Hypothyroidism - Hemochromatosis - Hypomagnesemia - Hypophosphatasia ANA (antinuclear antibody) is for SLE, RF (rheumatoid factor) is for rheumatoid ahritis and CPK (creatinine phosphokinase) is raised in dermatomyositis & polymyositis. So, among the given option only TSH is the relevant investigation in context of CPPD ahropathy as it may be associated with hypothyroidism. Hypothyroidism is more common in females. For fuher explanation of CPPD please refer to Nov 09 (Oho)