What percentage of patients with Graves' disease have positive Thyroid Peroxidase antibodies (TPO Ab)?

Prevalence of TPO Antibodies in Graves' Disease

Approximately 70-75% of patients with Graves' disease have positive thyroid peroxidase antibodies (TPO Ab). 1, 2

Prevalence Data and Patterns

• According to international guidelines, thyroid autoantibodies are detected in 80-85% of cases of autoimmune thyroid diseases, with TPO antibodies being one of the most common 1
• In specific studies of Graves' disease:
  • 71.1% of patients with Graves' disease were found to be TPO Ab positive in a large retrospective cohort study 3
  • 75% of patients with juvenile Graves' disease were found to have positive TPO Ab titers in a long-term follow-up study 4
  • 69% of patients with Graves' disease were TPO Ab-positive in another cohort study 5

Clinical Significance of TPO Antibodies in Graves' Disease

Diagnostic Value

• While TSH receptor antibodies (TRAb) are the primary diagnostic marker for Graves' disease, TPO antibodies provide additional information about the autoimmune thyroid process 2
• TPO antibodies can help distinguish Graves' disease from other causes of hyperthyroidism when present alongside TRAb 1

Relationship with Disease Course

• There appears to be a weak positive correlation (r=0.295) between TRAb and TPO antibody titers at the time of Graves' disease diagnosis 3
• TPO antibody status may influence treatment outcomes:
  • TPO antibody positivity at diagnosis was associated with reduced relapse rate after radioactive iodine therapy (13.9% vs. 24.6%) 6
  • TPO antibody-positive patients may develop hypothyroidism more frequently after radioactive iodine therapy (88% vs. 72%) 5

Impact on Relapse After Treatment

• Evidence regarding TPO antibodies as predictors of relapse after antithyroid drug therapy is mixed:
  • Some studies show no difference in relapse rates between TPO Ab-positive and TPO Ab-negative patients after antithyroid drug treatment 6, 3
  • Other research suggests that changes in TPO antibody titers during treatment might be useful for predicting relapse in certain patient subgroups 7

Clinical Implications

• When evaluating a patient with suspected Graves' disease, testing should include:

  • TSH, Free T4, and Free T3 as initial thyroid function tests 2
  • TSH receptor antibodies (TRAb) as the primary diagnostic marker for Graves' disease 2
  • TPO antibodies to provide additional information about the autoimmune process 1, 2

• TPO antibody status may be particularly relevant when considering radioactive iodine therapy, as it might help predict the likelihood of post-treatment hypothyroidism 5

• Monitoring changes in TPO antibody titers during antithyroid drug treatment may provide additional prognostic information in some patients 7

Common Pitfalls and Caveats

• While TPO antibodies are common in Graves' disease, their absence does not rule out the diagnosis
• TPO antibodies alone cannot distinguish between different autoimmune thyroid diseases (Graves' disease vs. Hashimoto's thyroiditis)
• TPO antibody status should not be used in isolation to guide treatment decisions, as evidence for their predictive value in treatment outcomes is still evolving