This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology metabolism, Subject name: Physiology
A 53-year-old woman presents with weight loss, increased appetite, sweating, palpitations, and preference for cold weather, hot, moist palms, and tremors. What is the best investigation for the clinical diagnosis of this patient? 
Select and explain. 
A. TSH levels, B. Autoimmune panel, C. Plasma catecholamines, D. Plasma Cortisol
A: TSH levels
Answer: A: TSH levels 
Explanation: Ans. A TSH levelsRef: CMDT 2019 page 1139This patient presents with classic signs and symptoms of hyperthyroidism. The increased Basal metabolic rate and calorigenesis explain the symptoms of the patient. These patients have highly suppressed TSH levels. The highlights of hyperthyroidism are:* Sweating, weight loss or gain, anxiety, palpitations, loose stools, heat intolerance, fatigue, menstrual irregularity.* Tachycardia; warm, moist skin; stare; tremor.* Graves disease: Majority have a palpable goiter (sometimes with bruit); ophthalmopathy.* Suppressed TSH in primary hyperthyroidism; usually increased T4 ,FT4 ,T3 ,FT3 .