During a routine health maintenance visit, a 32-year-old female patient mentions that she has been feeling unusually sluggish over the past few months. She reports a recent 4-kg (8.8-lb) weight gain, worsening constipation, and a constant feeling of being cold, even during the summer months. She has no chronic medical conditions and takes no prescription medications. Her vital signs show a temperature of 36.4°C (97.5°F), blood pressure of 112/74 mmHg, and a pulse of 54/min. Physical examination reveals noticeably dry skin and a prolonged relaxation phase of the Achilles tendon reflexes. Which of the following is the most appropriate initial diagnostic test to investigate this patient's symptoms?
- Serum thyroid-stimulating hormoneAnswer
- BSerum free thyroxine
- CSerum anti-thyroid peroxidase antibodies
- DFine-needle aspiration biopsy of the thyroid
- EMagnetic resonance imaging of the brain
Answer
The most appropriate initial diagnostic test is serum thyroid-stimulating hormone.
The patient's presentation of fatigue, weight gain, cold intolerance, bradycardia, and a delayed relaxation phase of deep tendon reflexes is classic for hypothyroidism. The most appropriate initial step in laboratory evaluation for suspected thyroid dysfunction is to measure serum thyroid-stimulating hormone (TSH). TSH is a highly sensitive assay; even minor changes in thyroid hormone levels lead to significant logarithmic inverse changes in TSH secretion. Therefore, it is the most reliable and cost-effective first-line test. If the TSH level is abnormal, subsequent testing with a serum free thyroxine (free T4) level is indicated to determine the severity and nature (primary versus central) of the disease.
Step-by-Step Solution
Key Concept
In patients with a classic clinical presentation of hypothyroidism, measuring serum thyroid-stimulating hormone (TSH) is the most sensitive and appropriate initial laboratory screening test.