What lab tests are recommended for diagnosing Hashimoto's (Hashimoto's thyroiditis) thyroiditis?

From the Guidelines

The primary lab tests recommended for diagnosing Hashimoto's thyroiditis include thyroid stimulating hormone (TSH), free T4, and thyroid antibodies, specifically thyroid peroxidase antibodies (TPOAb) and thyroglobulin antibodies (TgAb). When interpreting TSH results, it is essential to consider the reference range, which is defined as 0.45 to 4.5 mIU/L, as suggested by some investigators 1. Some key points to consider when ordering lab tests for Hashimoto's thyroiditis include:

• TSH is typically elevated in Hashimoto's while free T4 may be normal or low, depending on disease progression
• The presence of thyroid antibodies, particularly TPOAb which is positive in about 95% of cases, is the hallmark of this autoimmune condition
• TgAb is found in approximately 60-80% of patients
• Complete blood count and comprehensive metabolic panel may also be ordered to assess overall health status
• In some cases, physicians might recommend thyroid ultrasound to evaluate thyroid structure and identify characteristic heterogeneous appearance with hypoechoic areas These tests collectively help establish the diagnosis by confirming the presence of autoimmune activity against the thyroid gland and assessing the degree of thyroid dysfunction, as supported by guidelines for the diagnosis and management of subclinical thyroid disease 1. Regular monitoring of TSH and free T4 is important after diagnosis to guide treatment decisions, as Hashimoto's often progresses to hypothyroidism requiring thyroid hormone replacement therapy.

From the Research

Lab Tests for Diagnosing Hashimoto's Thyroiditis

To diagnose Hashimoto's thyroiditis, several lab tests are recommended, including:

• Thyroid function tests, such as:
  • Serum TSH (thyroid-stimulating hormone) concentrations, which are the most reliable and informative regarding thyroid function 2
  • FT4 (free thyroxine), which supersedes total T4 (TT4) due to its ability to depict within reference intervals despite changes in serum thyroid hormone binding proteins 2
  • FT3 (free triiodothyronine), although its measurement deserves no more significance than T3 2
• Tests to detect serum autoantibodies against thyroid tissues, such as:
  • TgAb (thyroglobulin antibodies) 3, 4, 5
  • TPOAb (thyroid peroxidase antibodies) 3, 4, 5, 6
• TSH receptor antibody tests, such as TRAb (TSH receptor antibody) and TSAb (thyroid-stimulating antibody), which can help differentiate Graves' disease from Hashimoto's thyroiditis 2, 5

Interpretation of Lab Results

The interpretation of lab results is crucial in diagnosing Hashimoto's thyroiditis. For example:

• Elevated TgAb levels have been associated with symptom burden in patients with Hashimoto's thyroiditis, suggesting a role of thyroid autoimmunity in clinical manifestations of the disease 3
• Decreased TSH levels and increased FT4 levels can indicate hypothyroidism, while increased TSH levels and decreased FT4 levels can indicate hyperthyroidism 2
• The presence of TPOAb and/or TgAb can confirm the diagnosis of Hashimoto's thyroiditis, although these antibodies do not necessarily cause hypothyroidism 5

Monitoring and Follow-up

Regular monitoring and follow-up are essential in managing Hashimoto's thyroiditis. This includes:

• Periodic measurement of TSH, FT4, and FT3 levels to assess thyroid function 2
• Monitoring of TgAb and TPOAb levels to assess the severity of the disease and response to treatment 3, 4, 6
• Ultrasound of the neck to assess thyroid volume and morphology 6