Clinical Information

Clinical Use

Thyroid peroxidase antibodies (TPOAb) are used:

• As a primary marker for autoimmune thyroid disease (e.g., Hashimoto thyroiditis, Graves disease)
• To differentiate autoimmune thyroid disorders from nonautoimmune causes of goiter or hypothyroidism

Clinical Background

Thyroid peroxidase (TPO) is a membrane-associated enzyme expressed in thyroid follicular cells and plays a key role in thyroid hormone synthesis by catalyzing iodination of tyrosine residues in thyroglobulin.

Autoimmune thyroid diseases are characterized by the production of antibodies against thyroid antigens, particularly TPO and thyroglobulin.

TPOAb are the most sensitive serologic marker for autoimmune thyroid disease:

• Present in approximately 90% of patients with Hashimoto thyroiditis
• Detected in 60–80% of patients with Graves disease

Interpretation

Autoimmune Thyroid Disease

• Detectable TPOAb supports the presence of autoimmune thyroid disease
• TPOAb is more sensitive than TgAb for this purpose
• Results should be interpreted in conjunction with:
  • TSH and thyroid hormone levels
  • Clinical findings

TPOAb positivity is not specific for a single disorder and may be seen in:

• Hashimoto thyroiditis
• Graves disease
• Other autoimmune conditions

Subclinical Hypothyroidism

• Detectable TPOAb is associated with an increased risk of progression to overt hypothyroidism
• Annual risk of progression is higher in TPOAb-positive individuals compared to antibody-negative individuals

TPOAb status may be used as a supportive factor in clinical decision-making, including consideration of treatment.

Additional Clinical Associations

• Detectable TPOAb may be present in individuals with normal thyroid function
• TPOAb positivity is associated with an increased likelihood of developing:
  • Overt hypothyroidism over time
  • Other autoimmune conditions
• There is a strong association between TPOAb positivity and histologic thyroiditis, although clinical disease may not be immediately apparent

Methodology Considerations

• Results are method-dependent and may vary between assay platforms
• Results from different methods should not be directly compared

Detectable TPOAb alone does not establish a diagnosis and should not be used in isolation