What is the recommended workup for possible autoimmune thyroiditis?

Workup for Possible Autoimmune Thyroiditis

Measure TSH, free T4, and anti-thyroid peroxidase (anti-TPO) antibodies as the essential initial laboratory tests for suspected autoimmune thyroiditis. 1, 2

Initial Laboratory Testing

Core Diagnostic Tests

• TSH is the primary screening test with sensitivity above 98% and specificity greater than 92% for detecting thyroid dysfunction 2
• Free T4 distinguishes between subclinical hypothyroidism (normal free T4) and overt hypothyroidism (low free T4), which is critical for determining treatment urgency 2
• Anti-TPO antibodies confirm autoimmune etiology and predict higher risk of progression to overt hypothyroidism (4.3% per year vs 2.6% in antibody-negative individuals) 2, 3

Additional Antibody Testing

• Thyroglobulin antibodies (TgAb) can be measured alongside anti-TPO, as patients with high titers are more likely to progress to hypothyroidism 4
• TSH receptor antibodies (TRAb) should be checked if thyrotoxicosis is present, as high titers predict persistent hyperthyroidism and may indicate Graves' disease rather than thyroiditis 1, 4
• Total IgE levels help distinguish autoimmune from autoallergic mechanisms—patients with autoimmune disease typically have low or very low total IgE with elevated anti-TPO 1

Imaging Studies

Thyroid Ultrasound

• Perform thyroid ultrasound to assess gland echogenicity and identify nodules, as autoimmune thyroiditis characteristically shows a hypoechoic pattern 5
• Evaluate for suspicious nodules requiring fine needle aspiration (FNA) based on size and ultrasound characteristics including microcalcifications, irregular borders, and central hypervascularity 1

Clinical Assessment Details

History Elements to Document

• Symptoms of hypothyroidism: unexplained fatigue, weight gain, hair loss, cold intolerance, constipation, depression 1, 2
• Symptoms of thyrotoxicosis: weight loss, palpitations, heat intolerance, tremors, anxiety, diarrhea (may occur in thyroiditis phase) 1
• Family history of thyroid disease or other autoimmune conditions increases pretest probability 1
• Recent pregnancy, miscarriage, or medical abortion within the past year suggests postpartum thyroiditis 3
• Medication history including amiodarone, immune checkpoint inhibitors, interleukin-2, interferon-alfa, lithium, or tyrosine kinase inhibitors that can induce thyroiditis 3

Physical Examination Findings

• Palpate for goiter, which is often painless in Hashimoto's thyroiditis 3
• Assess for thyroid tenderness, which characterizes subacute thyroiditis but is absent in Hashimoto's 3
• Check for signs of hypothyroidism: bradycardia, delayed relaxation phase of deep tendon reflexes, dry skin, periorbital edema 2

Confirmatory Testing Strategy

When to Repeat Testing

• Confirm elevated TSH with repeat testing after 3-6 weeks, as 30-60% of high TSH levels normalize spontaneously 2
• Recheck TSH and free T4 in 4-6 weeks after resolution of acute illness if initially abnormal during hospitalization or acute medical conditions 2

Additional Metabolic Assessment

• Comprehensive metabolic panel and CBC to exclude other causes of symptoms 1
• Lipid profile, as subclinical hypothyroidism may affect cholesterol levels 2
• Consider screening for other autoimmune conditions if anti-nuclear antibody (ANA) is positive, including anti-dsDNA, anti-scl-70, anti-centromere, anti-RNP, anti-SSA, anti-SSB 1

Common Diagnostic Pitfalls

• Do not treat based on a single elevated TSH value without confirmation, as transient elevations are common and frequently normalize 2
• Avoid missing central hypothyroidism by checking free T4 alongside TSH in patients with pituitary disease or symptoms despite normal TSH 2
• Never start thyroid hormone before ruling out adrenal insufficiency in patients with suspected central hypothyroidism or hypophysitis, as this can precipitate adrenal crisis 1, 2
• Recognize that anti-TPO antibodies are a hallmark of Hashimoto's thyroiditis but cannot predict initial presentation (euthyroid vs hypothyroid vs hyperthyroid) or clinical outcome 4
• Consider that most patients with autoimmune thyroiditis follow a triphasic pattern: initial thyrotoxicosis from hormone release, followed by hypothyroidism when stores are depleted, then potential recovery or permanent hypothyroidism 3