From the Guidelines
TPO antibodies (TPO ab) should be prioritized over thyroid-stimulating hormone receptor antibodies (TRAB) when suspecting Hashimoto's thyroiditis, while TRAB testing is indicated when Graves' disease is suspected, particularly in patients with hyperthyroidism, exophthalmos, or pretibial myxedema. TPO antibodies target thyroid peroxidase, an enzyme involved in thyroid hormone production, and are primarily used to diagnose Hashimoto's thyroiditis, the most common cause of hypothyroidism 1. Elevated TPO ab levels indicate autoimmune thyroid inflammation but don't necessarily correlate with thyroid function. TRAB, on the other hand, binds to TSH receptors on thyroid cells and is the hallmark of Graves' disease, the most common cause of hyperthyroidism 1.
When evaluating thyroid dysfunction, it is essential to consider the clinical presentation and laboratory results to determine the appropriate testing. According to the most recent guidelines 1, TPO ab testing is recommended when suspecting Hashimoto's thyroiditis, while TRAB testing is indicated when Graves' disease is suspected. Both tests can be ordered simultaneously in unclear cases of thyroid dysfunction to help determine the underlying autoimmune process. The management of thyroid dysfunction should be based on the underlying cause, and treatment options may include thyroid hormone replacement therapy, beta blockers, or other medications 1.
Key points to consider when evaluating TPO ab and TRAB include:
- Clinical presentation: Hyperthyroidism, hypothyroidism, exophthalmos, or pretibial myxedema
- Laboratory results: TSH, free T4, total T3, and thyroid autoantibodies
- Underlying cause: Hashimoto's thyroiditis, Graves' disease, or other thyroid disorders
- Treatment options: Thyroid hormone replacement therapy, beta blockers, or other medications 1.
From the Research
TPOAb vs TRAb
- TPOAb (thyroid peroxidase antibody) and TRAb (TSH receptor antibody) are two different types of antibodies associated with thyroid disorders 2, 3.
- TPOAb is commonly found in patients with Hashimoto's thyroiditis, an autoimmune thyroid disease characterized by hypothyroidism 2.
- TRAb, on the other hand, is associated with Graves' disease, an autoimmune thyroid disease characterized by hyperthyroidism 3, 4.
- The presence of TPOAb does not necessarily indicate hypothyroidism, as approximately 10% of individuals with positive TPOAb have hypothyroidism 2.
- TRAb is considered the gold standard diagnostic test for Graves' disease, with a sensitivity of 88% and specificity of 66% compared to clinical diagnosis 4.
Clinical Implications
- TPOAb detectability is associated with an increased risk of overall, cancer-related, and cardiovascular mortality, particularly in men 5.
- The epitope recognition pattern of TPOAb differs between healthy individuals and patients with Hashimoto's thyroiditis, with healthy individuals having a distinct distribution of IDR-A and IDR-B reactivity 6.
- The clinical importance of detectable TPOAb levels is illustrated by their association with increased mortality risk, potentially as a marker for low-grade inflammation 5.
Diagnostic Utility
- TPOAb and TRAb tests are used to diagnose Hashimoto's thyroiditis and Graves' disease, respectively 3.
- Clinicians should be aware of the possible pitfalls and caveats in the use of these tests, including assay interferences and the effects of concurrent medications 3.
- The TRAb test can help reduce the number of incorrect or unknown diagnoses in the initial clinical assessment of patients presenting with hyperthyroidism 4.