What is the role of lab testing in the diagnosis of subacute lymphocytic thyroiditis?

Updated: Mar 23, 2021
  • Author: Stephanie L Lee, MD, PhD; Chief Editor: Romesh Khardori, MD, PhD, FACP  more...
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The time course for subacute lymphocytic thyroiditis is identical to that for subacute granulomatous thyroiditis. Thyroid hormone levels are very elevated in subacute lymphocytic thyroiditis. The destructive phase of thyroiditis causes the release of preformed hormone stores in the thyroid. This form of thyroid hormone is highly iodinated, such that the release of hormone has a lower ratio of total T3 to total T4 than does Graves disease. A ratio of T3 to T4 of less than 15 usually increases suspicion of subacute thyroiditis.

As with subacute granulomatous thyroiditis, radioiodine uptake is less than 1% at 24 hours. However, the ESR is within the reference range and the thyroid is not painful in subacute lymphocytic thyroiditis, which distinguishes this condition from the other disease.

After the thyroid is depleted of thyroid hormone, patients' serum levels of T4 and T3 decrease into the hypothyroid range. The hypothyroidism is usually mild but persists for 2-4 months. Supplementation with thyroid hormone is necessary only if the patient becomes symptomatic.

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