Key takeaways
- TSH is the most sensitive first-line screen — a normal TSH makes significant thyroid dysfunction unlikely
- Subclinical hypothyroidism affects 5–10% of adults and is frequently undiagnosed
- Autoimmune thyroid disease (Hashimoto's) is the most common cause of hypothyroidism in iodine-sufficient regions
- Iodine deficiency remains the leading preventable cause of thyroid disease globally
- Thyroid nodules are common (found in ~50% of adults on ultrasound) and usually benign
Why thyroid disorders go undetected
The thyroid gland regulates metabolic rate, heart rate, body temperature, digestion, and brain development. Its symptoms — fatigue, weight changes, mood shifts, hair loss — are nonspecific and easily attributed to stress, aging, or lifestyle. This is why up to 60% of people with thyroid disease remain undiagnosed.
Who should be screened
Women over 60, anyone with a family history of thyroid disease, those with other autoimmune conditions, and anyone with symptoms consistent with thyroid dysfunction. TSH (thyroid-stimulating hormone) is the first-line test — a single blood draw. If abnormal, free T4 and thyroid antibodies are added.
Hypothyroidism: the underactive thyroid
Hashimoto thyroiditis — an autoimmune destruction of the thyroid — is responsible for 90% of hypothyroidism in iodine-sufficient countries. Treatment with levothyroxine is effective, inexpensive, and generally well tolerated. Optimal TSH target varies by age and clinical context.
Hyperthyroidism: the overactive thyroid
Graves disease accounts for 80% of hyperthyroidism. It raises heart rate, causes weight loss, anxiety, and heat intolerance, and — if untreated — can precipitate atrial fibrillation. Treatment options include antithyroid drugs, radioiodine, or surgery, depending on severity and patient preference.
Thyroid nodules and cancer
Thyroid nodules are found in approximately 50% of adults on ultrasound. Most are benign. Those larger than 1 cm or with suspicious ultrasound features warrant fine-needle aspiration biopsy. Thyroid cancer, when detected early (stage I–II), has a 10-year survival rate exceeding 95%.
Iodine and nutrition
Adequate iodine intake — primarily from iodized salt, seafood, and dairy — is essential for thyroid hormone synthesis. Both deficiency and excess are harmful. In areas where dietary iodine is uncertain, a standard multivitamin with iodine provides adequate supplementation.