What is the purpose of a Thyroid Antibody (Thyroid Autoantibody) test?

From the Guidelines

Thyroid antibody tests should be performed soon after the diagnosis of type 1 diabetes and if symptoms develop, as autoimmune thyroid disease is the most common autoimmune disorder associated with diabetes, occurring in 17–30% of individuals with type 1 diabetes 1. When considering thyroid antibody tests, it's essential to understand that they can indicate autoimmune thyroid disorders, such as Hashimoto's thyroiditis or Graves' disease. The test typically checks for thyroid peroxidase antibodies (TPOAb) and thyroglobulin antibodies (TgAb), which are commonly elevated in these conditions. According to a study in Diabetes Care, at the time of diagnosis, 25% of children with type 1 diabetes have thyroid autoantibodies, the presence of which is predictive of thyroid dysfunction—most commonly hypothyroidism, although hyperthyroidism occurs in 0.5% of people with type 1 diabetes 1. Some key points to consider when interpreting thyroid antibody test results include:

• Normal results generally show no antibodies or very low levels
• Elevated antibodies suggest your immune system is attacking your thyroid tissue
• Positive antibody results don't always mean you have active thyroid disease, but they indicate increased risk
• Thyroid function tests may be misleading if performed at the time of diagnosis due to the effect of previous hyperglycemia, ketosis or ketoacidosis, weight loss, etc., and should be repeated soon after a period of metabolic stability and achievement of glycemic targets 1. It's crucial to interpret these results alongside other thyroid function tests (TSH, T3, T4) and clinical symptoms to determine if treatment is necessary. Regular monitoring may be recommended if antibodies are detected but thyroid function remains normal, as this can help catch developing thyroid problems early. Subclinical hypothyroidism may be associated with an increased risk of symptomatic hypoglycemia and a reduced linear growth rate, while hyperthyroidism alters glucose metabolism and usually causes deterioration of glycemia 1.

From the Research

Thyroid Antibody Test

• The thyroid antibody test is used to diagnose autoimmune thyroid disease, which includes conditions such as Hashimoto's thyroiditis and Graves' disease 2.
• There are three major anti-thyroid antibodies: those directed against the TSH receptor (TRAb), against thyroid peroxidase (TPOAb), and against thyroglobulin (TgAb) 2.
• TRAb is a hallmark of Graves' disease and can predict response to disease treatment 2.
• TPOAb and TgAb can identify individuals with a higher risk of progression to hypothyroidism, and their positivity defines the presence of thyroid autoimmunity 2.

Comparison of Thyroid Antibodies

• A study compared the prevalence of TgAb and TPOAb in Hashimoto's thyroiditis, Graves' disease, painless thyroiditis, and healthy control subjects using five different immunoassay kits 3.
• The results showed that TgAb was more frequent than TPOAb in patients with Hashimoto's thyroiditis and painless thyroiditis 3.
• The study suggested that TgAb immunoassay is the first choice of screening test for thyroid autoimmune abnormalities 3.

Association with Symptom Burden

• A cross-sectional study found that TgAb levels were associated with symptom burden in patients with Hashimoto's thyroiditis 4.
• The study found a significant positive correlation between TgAb levels and the number of symptoms in HT patients without LT4 therapy 4.
• Elevated TgAb levels were associated with fragile hair, face edema, edema of the eyes, and harsh voice 4.

Clinical Utility

• Autoantibodies are useful in diagnosing Graves' disease and, to a lesser extent, autoimmune thyroid disease 5.
• TRAb levels >10 U/L increase the probability of Graves' disease by a moderate to large degree 5.
• A positive or negative TPOAb test increases or decreases the probability of autoimmune thyroid disease by only a small to moderate degree 5.

Autoantibody Tests

• A case-control study found that positive ANA and anti-DNA antibodies were more common in patients with Graves' disease than in controls 6.
• The study found that ANA by HEp-2 method was not found significantly more often in patients with Hashimoto's thyroiditis than in controls 6.
• The study concluded that no evidence of subclinical systemic autoimmune disease was found in patients with autoimmune thyroid disease 6.