To screen for hypothyroidism before diagnosing fibromyalgia, which test is commonly ordered?

• A. TSH (thyroid-stimulating hormone)
• B. ESR
• C. ANA
• D. Anti-CCP antibodies

Answer: (A)

Screening for hypothyroidism is important because its symptoms—fatigue, muscle aches, and cognitive slowing—can resemble fibromyalgia. The most appropriate initial test to screen thyroid function is TSH (thyroid-stimulating hormone) because it is the most sensitive indicator of thyroid status in most people. In primary hypothyroidism, the pituitary raises TSH in response to low thyroid hormone levels, so a high TSH points to thyroid dysfunction and prompts confirmation with a free T4 test. If TSH is normal, other causes for the symptoms can be considered. The other tests—ESR, ANA, and anti-CCP—assess inflammation or autoimmune diseases and do not screen for thyroid problems. Thus, TSH is the best initial screen.