Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1236 page)

   Thyroid receptor antibodies mainly used in Graves disease, especially as a predictor of relapse of hyperthyroidism

   Interpretation

   Positive in approximately 95% of cases of Hashimoto disease and approximately 85% of Graves disease. Very high titer is suggestive of Hashimoto thyroiditis but absence does not exclude Hashimoto thyroiditis. Less than 1:1,000 occurs virtually only in Graves disease or Hashimoto thyroiditis.

Increased In

   Significant titer of microsome antibodies indicates Hashimoto thyroiditis or postpartum thyroiditis.

   Significant titer of antibodies in euthyroid patient with unilateral exophthalmos suggests the diagnosis of euthyroid Graves disease. Elevated antibody titer in a patient with Graves disease should direct a surgeon to perform a more limited thyroidectomy to avoid late postthyroidectomy hypothyroidism.

   Occasionally positive in papillary–follicular carcinoma of the thyroid, subacute thyroiditis (briefly), and lymphocytic (painless) thyroiditis (in approximately 60% of patients).

   Primary thyroid lymphoma often shows very high titers. This result should suggest need for biopsy in elderly patient with a firm enlarging thyroid.

   Low titers are present in >10% of normal population, increasing with age.

   Other autoimmune diseases (e.g., PA, RA, SLE, myasthenia gravis).

Decreased In

   In the absence of antibodies, Hashimoto thyroiditis is very unlikely cause of hypothyroidism.

   Limitations

   Tg antibodies may interfere with assay for serum Tg.

THYROID HORMONE–BINDING RATIO (THBR)

   Definition