What blood tests are used to diagnose thyroiditis (inflammation of the thyroid gland)?

From the Guidelines

Blood tests for thyroiditis typically include thyroid function tests and antibody tests, with the primary tests being TSH, free T4, free T3, anti-thyroid peroxidase antibodies (anti-TPO), and anti-thyroglobulin antibodies (anti-Tg) 1.

Diagnosis of Thyroiditis

The diagnosis of thyroiditis involves a combination of clinical evaluation and laboratory tests.

• Thyroid function tests, such as TSH, free T4, and free T3, are used to assess the functional status of the thyroid gland.
• Antibody tests, including anti-TPO and anti-Tg, help identify autoimmune thyroiditis, with anti-TPO being more predictive than anti-Tg in multivariate analysis 1.
• Inflammatory markers like ESR and CRP may be elevated in subacute thyroiditis.
• Complete blood count and liver function tests can provide additional information on the patient's overall health status.

Interpretation of Test Results

• An elevated TSH with low free T4 indicates hypothyroidism, while low TSH with high free T4 suggests hyperthyroidism, both of which can occur in thyroiditis.
• The presence of anti-TPO or anti-Tg antibodies strongly supports autoimmune thyroiditis (Hashimoto's thyroiditis), the most common form.
• Testing should be interpreted in the context of clinical symptoms, as thyroid antibodies can sometimes be present in people without clinical disease.

Treatment and Management

• Appropriate treatment may include thyroid hormone replacement for hypothyroidism or beta-blockers for hyperthyroidism symptoms.
• For patients with immune-related adverse events, such as those treated with immune checkpoint inhibitors, management of thyroiditis may involve holding or continuing immunotherapy, depending on the severity of symptoms, and initiating thyroid hormone supplementation as needed 1.
• Conservative management during the thyrotoxic phase of thyroiditis is often sufficient, with non-selective beta blockers used in symptomatic patients, and thyroid hormone replacement initiated at the time of hypothyroidism diagnosis 1.

From the Research

Blood Tests for Diagnosing Thyroiditis

The following blood tests are used to diagnose thyroiditis:

• Thyroid function tests, including:
  • Thyroid-stimulating hormone (TSH) levels 2, 3, 4
  • Free thyroxine (FT4) levels 2, 3, 4
  • Free triiodothyronine (FT3) levels 2, 3, 4
• Autoantibody tests, including:
  • Thyroid peroxidase antibodies (TPO-Ab) 2, 5, 4
  • Thyroglobulin antibodies (Tg-Ab) 2, 5, 4
  • TSH receptor antibodies (TRAb) 2, 5, 4
• Other tests, including:
  • Thyroglobulin (Tg) levels 3, 4
  • Calcitonin levels 3, 4

Interpretation of Test Results

When interpreting the results of these blood tests, it is essential to consider the clinical context and potential pitfalls, such as:

• Assay interferences 4
• Effects of concurrent medications 4
• Changes in thyroid function during pregnancy and critical illness 4
• Discordant results, which may require further evaluation 4

Specific Tests for Thyroiditis

For patients with suspected thyroiditis, the following tests may be particularly useful:

• TSH levels to assess thyroid function 2, 3, 4
• TPO-Ab and Tg-Ab tests to diagnose autoimmune thyroiditis 2, 5, 4
• TRAb tests to diagnose Graves' disease 2, 5, 4