Is TPO (thyroid peroxidase) antibody high in Graves' disease or Hashimoto's thyroiditis?

TPO Antibodies in Graves' Disease and Hashimoto's Thyroiditis

TPO (thyroid peroxidase) antibodies are primarily elevated in Hashimoto's thyroiditis, with nearly 99% of Hashimoto's patients testing positive, while they are present in about 74% of Graves' disease patients, though typically at lower concentrations. 1

Antibody Patterns in Autoimmune Thyroid Diseases

Hashimoto's Thyroiditis

• TPO antibodies are the hallmark of Hashimoto's thyroiditis, with:
  • Positive in 99.3% of patients with Hashimoto's thyroiditis or idiopathic myxedema 1
  • Typically higher concentrations than in Graves' disease (range 11-90,000 U/mL) 1
  • Highest concentrations found in untreated hypothyroid Hashimoto's thyroiditis 1
  • TPO antibodies may decrease with levothyroxine treatment, but only become negative in about 16% of patients even after long-term treatment 2

Graves' Disease

• TPO antibodies are present but less universal:
  • Positive in 74% of Graves' disease patients 1
  • Generally lower concentrations than in Hashimoto's (range 11-74,000 U/mL) 1
  • TSH receptor antibodies (TRAb) are the primary antibodies in Graves' disease 3
  • Anti-TPO levels typically decrease by over 50% after achieving euthyroid state with treatment 4

Clinical Significance of TPO Antibodies

• TPO antibodies have high specificity for autoimmune thyroid disease, with only 8.4% of normal controls showing low-level positivity 1

• Using a cut-off of 200 U/mL provides:

  • 96% sensitivity for Hashimoto's thyroiditis
  • 59% sensitivity for Graves' disease
  • 100% specificity for autoimmune thyroid disease 4

• High TPO antibody levels correlate with increased symptom burden even in euthyroid patients, including:

  • Chronic fatigue
  • Dry hair
  • Chronic irritability and nervousness
  • Lower quality of life scores 5

Disease Evolution and Antibody Changes

• Some patients with Graves' disease may develop Hashimoto's thyroiditis over time (15-20%) 6
• This transition can occur months to years after treatment for Graves' disease 6
• The shift may represent an extended immune response that initially targets TSH receptors and later expands to include thyroid peroxidase and thyroglobulin 6

Diagnostic Approach

When evaluating thyroid autoimmunity, a comprehensive antibody panel should include:

1. TSH, Free T4, and Free T3 to assess thyroid function 3
2. TPO antibodies - primary marker for Hashimoto's, also present in many Graves' patients 3
3. TSH receptor antibodies (TRAb) - specific for Graves' disease 3
4. Thyroglobulin antibodies - supplementary marker for autoimmune thyroid disease 3

Monitoring Considerations

• TPO antibody levels may decrease with treatment:
  • In Graves' disease: median decrease >50% after achieving euthyroid state 4
  • In Hashimoto's: variable response to levothyroxine, with an average 45% decrease after 1 year and 70% after 5 years 2
• Persistently elevated TPO antibodies may indicate ongoing autoimmune activity even when thyroid function tests are normal 5

In summary, while both conditions are autoimmune thyroid diseases, TPO antibodies are more characteristic of and found at higher concentrations in Hashimoto's thyroiditis, though they are also present in a majority of Graves' disease patients.