From the Guidelines
Elevated Antithyroglobulin (ATG) antibodies with normal Thyroid Peroxidase (TPO) antibodies in a workup for subclinical hypothyroidism may indicate an autoimmune etiology, but the presence or absence of these antibodies does not change the diagnosis or treatment of subclinical hypothyroidism, which is based on serum TSH measurements 1.
Key Points
- The presence of anti-TPO antibodies, not ATG antibodies, predicts a higher risk of developing overt hypothyroidism (4.3% per year vs 2.6% per year in antibody-negative individuals) 1.
- Approximately 2% to 5% of patients with subclinical hypothyroidism will progress to overt hypothyroidism per year, with a higher rate in individuals with antithyroid antibodies 1.
- The diagnosis of subclinical hypothyroidism is based on serum TSH measurements, and the presence or absence of antibodies does not affect the expected efficacy of treatment 1.
Clinical Implications
- Elevated ATG antibodies with normal TPO antibodies may not be a strong predictor of autoimmune etiology or progression to overt hypothyroidism.
- Serum TSH measurements remain the primary diagnostic tool for subclinical hypothyroidism.
- Patients with subclinical hypothyroidism should be monitored regularly for progression to overt hypothyroidism, regardless of antibody status 1.
From the Research
Significance of Elevated Antithyroglobulin (ATG) Antibodies and Normal Thyroid Peroxidase (TPO) Antibodies
- Elevated ATG antibodies and normal TPO antibodies in a workup for subclinical hypothyroidism may indicate the presence of autoimmune thyroiditis, specifically Hashimoto's thyroiditis 2.
- The presence of ATG antibodies has been associated with symptom burden in patients with Hashimoto's thyroiditis, including fragile hair, face edema, edema of the eyes, and harsh voice 2.
- Studies have shown that ATG antibodies are positively correlated with thyroid volume and negatively correlated with FT3 levels, suggesting a role in thyroid dysfunction 3, 4.
- The correlation between ATG antibodies and TSH, T3, and T4 hormones is significant, indicating that ATG antibodies may be useful in the diagnosis and monitoring of autoimmune thyroid disorders 5.
Clinical Implications
- Elevated ATG antibodies and normal TPO antibodies may indicate a higher risk of subclinical hypothyroidism, particularly in areas with high water iodine concentrations 3.
- The presence of ATG antibodies may be associated with an increased risk of thyroid enlargement and thyroid dysfunction, particularly in women 6, 4.
- Screening for ATG antibodies may be beneficial in patients with symptom burden and suspected autoimmune thyroid disorders, particularly in those with normal TPO antibodies 2.
Associations with Thyroid Function and Structure
- Elevated ATG antibodies have been associated with abnormal thyroid function and structure, including thyroid hypo- and heteroechogenicity 4.
- The presence of ATG antibodies has been linked to an increased risk of thyroid autoimmunity, particularly in women with thyroid enlargement and hypoechogenicity 4.
- The correlation between ATG antibodies and thyroid function test parameters, including TSH, T3, and T4, is significant, indicating a role in thyroid dysfunction 5.