## Autoimmune Antibodies in Thyroiditis **Key Point:** Anti-thyroid peroxidase (anti-TPO) antibody is the most specific and sensitive marker for Hashimoto's thyroiditis, present in 90–95% of patients and correlating with disease severity and progression. ### Antibody Profile in Thyroid Autoimmunity | Antibody | Hashimoto's | Graves' | Subacute | Sensitivity | Specificity | |----------|-------------|---------|----------|-------------|-------------| | **Anti-TPO** | +++++ | + | − | 90–95% | Very high | | **Anti-thyroglobulin** | ++++ | + | − | 60–70% | Moderate | | **TRAb (anti-TSH-R)** | − | +++++ | − | 90% | Very high | | **Anti-smooth muscle** | − | − | − | Non-specific | Low | **High-Yield:** TPO (thyroid peroxidase) is the enzyme responsible for iodination of tyrosine residues in thyroglobulin. Antibodies against TPO are the primary driver of thyroid destruction in Hashimoto's thyroiditis through complement-dependent and antibody-dependent cellular cytotoxicity (ADCC). **Mnemonic:** **TPO = Thyroid Peroxidase = Hashimoto's** — Remember that anti-TPO is the hallmark of Hashimoto's, while anti-TSH receptor (TRAb) is the hallmark of Graves' disease. ### Clinical Significance 1. **Diagnostic value**: Anti-TPO positivity confirms autoimmune thyroiditis 2. **Disease activity**: Titers correlate with degree of lymphocytic infiltration and thyroid dysfunction 3. **Predictive value**: Presence of anti-TPO in euthyroid individuals predicts future development of hypothyroidism 4. **Pregnancy implications**: Anti-TPO positivity increases risk of postpartum thyroiditis **Clinical Pearl:** Anti-thyroglobulin antibodies are also present in Hashimoto's but are less specific and less sensitive than anti-TPO. Both may coexist, but anti-TPO alone is sufficient for diagnosis.
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.