Laboratory tests most useful in confirming a diagnosis of De Quervain's thyroiditis in primary care include measurement of thyroid function tests, specifically TSH, free T4 (FT4), and free T3 (FT3). Typically, De Quervain's thyroiditis presents with transient thyrotoxicosis characterized by suppressed TSH and elevated FT4 and FT3 levels due to thyroid inflammation and hormone leakage.
Additional supportive tests include inflammatory markers such as erythrocyte sedimentation rate (ESR) or C-reactive protein (CRP), which are usually elevated in De Quervain's thyroiditis reflecting the inflammatory process.
Thyroid autoantibodies (such as TPO antibodies and TSH receptor antibodies) are generally negative or low, helping to differentiate De Quervain's thyroiditis from autoimmune thyroid diseases like Graves' disease or Hashimoto's thyroiditis.
Measurement of TSH receptor antibodies (TRAbs) is useful to exclude Graves' disease if thyrotoxicosis is present.
Ultrasound imaging may be considered if there is diagnostic uncertainty or to exclude nodules, but the primary diagnosis relies on clinical presentation and laboratory thyroid function and inflammatory markers.
These recommendations align with NICE guidance on thyroid disease assessment and management, which emphasises thyroid function tests and antibody testing to differentiate causes of thyrotoxicosis and thyroiditis in primary care NICE NG145.