Should I check thyroid antibodies and ultrasound (US) of the thyroid?

Thyroid Antibodies and Ultrasound Testing Recommendations

Testing for thyroid antibodies and performing thyroid ultrasound should be based on clinical suspicion of thyroid disease, with antibody testing recommended for suspected autoimmune thyroid disease and ultrasound primarily indicated for structural abnormalities or follow-up of thyroid cancer.

Thyroid Antibody Testing

When to Check Thyroid Antibodies:

• Consider testing for antithyroid peroxidase (TPO) and antithyroglobulin (TG) antibodies soon after diagnosis of type 1 diabetes, as autoimmune thyroid disease occurs in 17-30% of these patients 1
• TPOAb testing is more predictive than TgAb for identifying autoimmune thyroid disease 1
• Antibody testing is valuable for diagnosing autoimmune thyroid conditions, with >99% of spontaneously hypothyroid patients testing positive for either TPOAb or TgAb 2
• TPOAb is more frequently positive than TgAb in autoimmune hypothyroidism (95.9% vs 80.7%) 2
• Elevated antibodies help identify individuals at higher risk of progression to hypothyroidism 3

Clinical Utility of Specific Antibodies:

• TPOAb and TgAb indicate thyroid autoimmunity and are useful in diagnosing Hashimoto's thyroiditis 3
• TSH receptor antibodies (TRAb) are the hallmark of Graves' disease and help predict treatment response 4
• Clearly elevated anti-TPO values (>500 units/ml) are found in 59% of patients with thyroiditis but not in controls or patients with non-thyroidal illness 5
• Antibody testing has high specificity (100%) for autoimmune thyroid disease when using appropriate cutoffs 5

Thyroid Ultrasound

When to Perform Thyroid Ultrasound:

• Ultrasound is the most effective tool for detecting structural disease in the neck, particularly when remnants of normal thyroid tissue are present 1
• Neck ultrasound is indicated for evaluation of palpable thyroid abnormalities or deeper neck masses that are not palpable 1
• In thyroid cancer patients, ultrasound is essential for post-operative monitoring at 6-12 months and then periodically based on risk stratification 1
• Ultrasound findings can be classified as normal, indeterminate, or suspicious based on specific characteristics 1

Limitations of Thyroid Ultrasound:

• Ultrasound has substantial operator dependency and may show non-specific findings 1
• It may provide unsatisfactory visualization of deep structures and those acoustically shadowed by bone or air 1
• For these limitations, cross-sectional imaging modalities may be more appropriate 1

Specific Clinical Scenarios

For Patients with Type 1 Diabetes:

• Test for antithyroid peroxidase and antithyroglobulin antibodies soon after diagnosis 1
• Measure thyroid-stimulating hormone (TSH) at diagnosis when clinically stable or after glycemic control is established 1
• If normal, consider rechecking every 1-2 years or sooner if symptoms of thyroid dysfunction develop 1

For Suspected Autoimmune Thyroid Disease:

• TPOAb testing has 96% sensitivity for Hashimoto's thyroiditis and 59% for Graves' disease with 100% specificity using a cutoff of 200 units/ml 5
• Combined antibody testing (TPOAb and TgAb) provides the highest diagnostic accuracy for autoimmune thyroid conditions 2

For Thyroid Cancer Surveillance:

• Neck ultrasound should be performed at 6-12 months post-treatment and then periodically based on risk stratification 1
• Ultrasound combined with serum thyroglobulin measurement provides the most accurate follow-up strategy 1
• Suspicious ultrasound findings warrant further investigation with fine needle aspiration cytology 1

Common Pitfalls and Caveats

• Thyroid function tests may be misleading if performed during acute illness (euthyroid sick syndrome) 1
• If performed at diagnosis and slightly abnormal, thyroid function tests should be repeated after a period of metabolic stability 1
• Isolated measurements of serum thyroglobulin cannot be reliably interpreted in the presence of normal thyroid tissue 1
• TgAb presence can interfere with thyroglobulin assays used for thyroid cancer monitoring 3
• Antibody levels may decrease after treatment of autoimmune thyroid disease, with variable patterns among patients 5

In conclusion, thyroid antibody testing is valuable for diagnosing autoimmune thyroid disease and identifying patients at risk for progression to hypothyroidism, while ultrasound is most useful for evaluating structural abnormalities and monitoring thyroid cancer. The decision to perform these tests should be guided by clinical presentation and risk factors.