From the Guidelines
To diagnose Hashimoto's thyroiditis, the primary antibodies to check are thyroid peroxidase antibodies (TPOAb) and thyroglobulin antibodies (TgAb). These tests are typically ordered alongside thyroid function tests, including thyroid-stimulating hormone (TSH), free T4, and sometimes free T3, to assess thyroid function status. The presence of elevated TPOAb and/or TgAb, especially when combined with clinical symptoms and abnormal thyroid function tests, strongly supports a diagnosis of Hashimoto's thyroiditis. These antibodies indicate an autoimmune process where the immune system is attacking the thyroid gland, leading to inflammation and potentially gradual destruction of thyroid tissue. Testing is done through a simple blood draw, and no special preparation is needed before the test. Regular monitoring of both antibody levels and thyroid function may be recommended to track disease progression and adjust treatment as needed, as suggested by the most recent guidelines 1. Some key points to consider include:
- TPOAb is the most sensitive marker, present in about 95% of patients with Hashimoto's, while TgAb is found in approximately 60-80% of cases.
- The presence of thyroid autoantibodies is predictive of thyroid dysfunction, most commonly hypothyroidism, although hyperthyroidism occurs in less than 0.5% of patients with type 1 diabetes 1.
- 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 good glycemic control 1. It's also important to note that autoimmune thyroid disease is the most common autoimmune disorder associated with diabetes, occurring in 17–30% of patients with type 1 diabetes 1. Overall, checking TPOAb and TgAb is crucial for diagnosing Hashimoto's thyroiditis, and should be done in conjunction with thyroid function tests and clinical evaluation.
From the Research
Antibodies to Check for Hashimoto Thyroiditis
The following antibodies are relevant to check for Hashimoto thyroiditis:
- Thyroglobulin antibodies (TgAb) 2, 3, 4
- Thyroid peroxidase antibodies (TPOAb) 2, 5, 3, 4, 6
- Thyroid-stimulating hormone (TSH)-stimulation blocking antibody (TSBAb) or TSH-receptor antibody (TRAb) 4
Prevalence of Antibodies
- TgAb prevalence is higher than TPOAb prevalence in patients with Hashimoto's thyroiditis and painless thyroiditis 3
- TPOAb levels decline in most patients with Hashimoto's thyroiditis who are taking levothyroxine, but TPOAb levels become negative in only a minority of patients 5
Clinical Significance
- Elevated TgAb levels are associated with symptom burden in Hashimoto's thyroiditis patients 2
- Presence of TPOAbs is associated with a 2 to 4-fold increase in the risk of recurrent miscarriages and preterm birth in pregnant women 6
- TgAb and/or TPOAb do not necessarily cause hypothyroidism, but are used to diagnose Hashimoto's thyroiditis 4