No Interference by Diclofenac with the New Vitros FT3II Assay Reagent

Measurements of serum concentrations of free triiodothyronine (FT3), thyroid-stimulating hormone (TSH), and free thyroxine (FT4) are useful in the diagnosis and treatment of thyroid diseases. Several nonsteroidal antiinflammatory drugs (NSAIDs) are known to interfere with thyroid function tests (1)(2). Cross-reaction with the assay antibody is one of the mechanisms of NSAID interference (3). The FT3 antibody included in the Vitros FT3 assay (Ortho-Clinical Diagnostics Inc.) cross-reacts with diclofenac, a phenylacetic acid derivative with structural resemblance to T3 (4). To avoid interference by diclofenac, …