What is the significance of anti-thyroid peroxidase (anti-TPO) antibodies?

From the Guidelines

The presence of anti-thyroid peroxidase (anti-TPO) antibodies is a significant indicator of autoimmune thyroid disease, particularly Hashimoto's thyroiditis, and warrants regular monitoring of thyroid function due to the increased risk of developing hypothyroidism.

Significance of Anti-TPO Antibodies

The presence of anti-TPO antibodies indicates an autoimmune process where the immune system mistakenly identifies thyroid peroxidase, an enzyme involved in thyroid hormone production, as foreign and attacks it, gradually destroying thyroid tissue and reducing hormone production [ 1 ].

Clinical Implications

Key points to consider include:

• Autoimmune thyroid disease is the most common autoimmune disorder associated with diabetes, occurring in 17–30% of patients with type 1 diabetes [ 1 ].
• At the time of diagnosis, approximately 25% of children with type 1 diabetes have thyroid autoantibodies, which are predictive of thyroid dysfunction, most commonly hypothyroidism [ 1 ].
• The presence of anti-TPO antibodies suggests an increased risk for developing hypothyroidism in the future, even with normal thyroid function currently, and thus warrants regular monitoring [ 1 ].

Management and Monitoring

Regular monitoring of thyroid function (TSH, free T4) is essential, typically every 6-12 months once stabilized. While anti-TPO levels themselves are not typically treated directly, managing the resulting hypothyroidism is crucial. Normal treatment involves thyroid hormone replacement, typically with levothyroxine at doses individualized to the patient's needs [ 1 ].

Recommendations

Consider testing children with type 1 diabetes for antithyroid peroxidase and antithyroglobulin antibodies soon after diagnosis, and measure thyroid-stimulating hormone concentrations at diagnosis when clinically stable or soon after glycemic control has been established [ 1 ]. If normal, suggest rechecking every 1–2 years or sooner if the patient has positive thyroid antibodies or develops symptoms or signs suggestive of thyroid dysfunction [ 1 ].

From the Research

Significance of Anti-Thyroid Peroxidase (Anti-TPO) Antibodies

• Anti-TPO antibodies are a significant indicator of autoimmune thyroiditis and are often associated with hypothyroidism 2, 3, 4, 5.
• The presence of anti-TPO antibodies can indicate a higher likelihood of progression to overt hypothyroidism, especially in patients with subclinical hypothyroidism 2, 3.
• Studies have shown that anti-TPO antibody positivity is a strong predictor of development of hypothyroidism, particularly in females with TSH levels above 6.9 mIU/L 3.
• The association between anti-TPO antibodies and thyroid stimulating hormone (TSH) values can be useful in determining the influence of latent thyroid gland damage on the requirement of TSH 6.
• Anti-TPO antibodies have been found to be more frequently measurable than thyroglobulin antibodies (TgAb) in patients with spontaneous hypothyroidism, and both antibodies are positively associated with thyroid enlargement 5.
• The presence of anti-TPO antibodies can also be an indicator of cardiovascular risk factors, as they have been associated with atherosclerosis in euthyroid individuals 6.

Clinical Implications

• Patients with positive anti-TPO antibodies and subclinical hypothyroidism may require closer monitoring and potentially earlier treatment to prevent progression to overt hypothyroidism 2, 3.
• The measurement of anti-TPO antibodies can be a useful tool in the diagnosis and management of thyroid disease, particularly in patients with autoimmune thyroiditis 4, 5.
• Further research is needed to fully understand the relationship between anti-TPO antibodies and cardiovascular risk factors, as well as the optimal management of patients with positive anti-TPO antibodies and subclinical hypothyroidism 2, 6.