A 40-year-old woman comes to the office for evaluation of significant fatigue, weight gain, and constipation over the past two months. She was diagnosed with hypothyroidism 5 years ago and has been taking a stable dose of levothyroxine with good adherence. Her last TSH level 6 months ago was within normal limits. She has not experienced any recent stressors or illnesses, and her medical history is otherwise unremarkable. She started taking an oral contraceptive pill 4 months ago. She does not drink alcohol, smoke cigarettes, or use illicit drugs. Her body mass index is 30 kg/m2, blood pressure is 130/80 mm Hg, and pulse is 72/min. On physical examination, the thyroid gland is nonpalpable, and there are no other significant findings on examination. Laboratory results are as follows:
- Sodium: 140 mEq/L
- Potassium: 4.2 mEq/L
- Glucose: 88 mg/dL
- Serum creatinine: 0.8 mg/dL
- Thyroid stimulating hormone (TSH): 8.5 µU/mL (normal 0.5-5.0 µU/mL)
Which of the following is the most likely cause of her current symptoms?
- A) Decreased absorption of levothyroxine
- B) Decreased levothyroxine dose requirement
- C) Increased hepatic metabolism of thyroid hormone
- D) Increased thyroxine-binding globulin concentration
- E) Interference of oral contraceptive with levothyroxine action
Author(s)
Kamand Khalaj
Editor(s)
Dr. Ted O'Connell
Last updated
Oct 14, 2024
