When is thyroid antibody testing recommended, especially in patients with suspected autoimmune thyroid disease or a family history of thyroid disorders?

Thyroid Antibody Testing: When and Who to Test

Thyroid antibody testing should be performed in high-risk populations rather than as routine screening, specifically targeting patients with type 1 diabetes, family history of thyroid disease, personal history of autoimmune disorders, prior thyroid dysfunction, or symptoms suggestive of thyroid disease. 1

High-Risk Groups Requiring Antibody Testing

Patients with Type 1 Diabetes

• Test for anti-thyroid peroxidase (anti-TPO) and anti-thyroglobulin antibodies soon after diabetes diagnosis 1, 2
• Anti-TPO antibodies are more predictive of future thyroid dysfunction than anti-thyroglobulin antibodies 1, 2
• Approximately 25% of children with type 1 diabetes have thyroid autoantibodies at diagnosis, and 17-30% will develop autoimmune thyroid disease 1
• The presence of antibodies indicates autoimmune thyroid disease is already present, even if thyroid function remains normal 2

Other High-Risk Populations Warranting Testing

• Women older than 60 years 1
• Patients with personal history of autoimmune disease 1
• Family history of thyroid disease 1
• Previous thyroid surgery or thyroid dysfunction 1
• Previous radiation treatment of the thyroid gland (radioactive iodine or therapeutic external beam radiation) 1
• Atrial fibrillation 1
• Palpable thyroid abnormalities or thyromegaly 1

Clinical Scenarios Requiring Antibody Testing

Symptomatic Patients

• Test patients presenting with signs or symptoms suggestive of hypothyroidism (fatigue, weight gain, mental slowing) or hyperthyroidism (weight loss, palpitations, tremor) 1
• Check antibodies when unexplained glycemic variability occurs in diabetic patients 1, 2
• Test when abnormal growth rate develops in children 1

Pregnancy Considerations

• Consider TSH and antibody testing in women planning pregnancy or currently pregnant who have family history of thyroid disease, prior thyroid dysfunction, symptoms of thyroid disease, abnormal thyroid examination, type 1 diabetes, or personal history of autoimmune disorder 1
• Evidence is insufficient to recommend routine screening in all pregnant women 1

Which Antibodies to Order

Primary Testing

• Anti-thyroid peroxidase (anti-TPO) antibodies are the most important initial test 2, 3
• Anti-TPO is more predictive than anti-thyroglobulin antibodies for future thyroid dysfunction 1, 2
• Anti-TPO positivity defines the presence of thyroid autoimmunity 3

Additional Antibody Testing

• Anti-thyroglobulin antibodies should be checked in patients with suspected autoimmune thyroid disease who are anti-TPO negative 3, 4
• TSH receptor antibodies (TRAb) are the hallmark of Graves' disease and should be measured in patients with hyperthyroidism to differentiate Graves' disease from other causes 5, 3, 6
• TRAb and thyroid-stimulating antibodies (TSAb) are useful for diagnosing and following patients with Graves' disease 5

Monitoring After Positive Antibody Results

Follow-Up Testing Schedule

• Measure TSH and free T4 every 1-2 years if antibody-positive with normal thyroid function 2
• Check more frequently (every 6-12 months) if symptoms develop, such as unexplained fatigue, weight changes, or hair loss 2
• In children with type 1 diabetes and positive antibodies, recheck TSH every 1-2 years or sooner if symptoms, thyromegaly, abnormal growth rate, or unexplained glycemic variability develops 1, 2

Critical Timing Considerations

• Always test in the morning when clinically stable, not during acute illness, as metabolic stress causes misleading results 2
• Thyroid function tests may be misleading (euthyroid sick syndrome) if performed during hyperglycemia, ketosis, ketoacidosis, or weight loss 1
• If performed at diagnosis and slightly abnormal, repeat thyroid function tests after achieving metabolic stability 1

What NOT to Do

Population Screening is Not Recommended

• Do not perform population-based screening for thyroid disease in asymptomatic individuals without risk factors 1
• The evidence does not support improved health outcomes from screening asymptomatic persons without risk factors 1

Common Pitfalls to Avoid

• Do not ignore mild antibody elevations in high-risk patients—antibody presence predicts future thyroid dysfunction even when thyroid function is currently normal 2, 3
• Do not test during acute non-thyroid illness, as severe illness can cause false positive TSH results 1
• Do not dismiss the need for antibody testing in patients on immune checkpoint inhibitors, as thyroid dysfunction occurs in 6-20% of these patients 2