Review symptoms and medical history
Perform a physical examination
Order thyroid-stimulating hormone (TSH) test
Order free thyroxine (free T4) test
Consider free triiodothyronine (free T3) test if needed
Check thyroid peroxidase antibodies (TPOAb) for autoimmune thyroiditis
Repeat abnormal thyroid tests to confirm results
Assess for pituitary or hypothalamic causes if TSH is not elevated
Review medications that can affect thyroid function
Evaluate for goiter or thyroid enlargement
Consider thyroid ultrasound if structural disease is suspected
Diagnose based on symptoms plus laboratory findings