A 42-year-old woman presents to your office because she has a ‘ton of problems to discuss’. She feels tired and fatigued all the time. She gained 10 pounds over the last month despite no change in eating habits. She is frequently cold when others are not. She takes high fiber pills everyday but can’t get rid of constipation. She has noticed a swelling sensation in her neck area. She has been having heavy irregular menses with lots of abdominal pain. She feels short of breath even for a short walk. She denies smoking, alcohol use and drug use. Her family history is significant for rheumatoid arthritis in her father and systemic lupus erythematosus in her mother. She was born in Lineville, Alabama. On examination, she looks anxious. Her vital signs are Her temperature is 96 °F,, heart rate is 58 beats/min, blood pressure is 148/98 mm Hg, respirations are 19 breaths/min, and oxygen saturation is 97% on room air.She has an enlarged, nontender thyroid noted on her neck.Her reflexes are delayed and diminished, and her skin is dry to the touch.She has proximal muscle weakness. You suspected hypothyroidism in this patient. Which of the following tests is the most sensitive test for detecting hypothyroidism?
