ANTIBODY INTERFERENCE IN THYROID ASSAYS - A POTENTIAL FOR CLINICAL MISINFORMATION

Measurements of thyrotropin and of total and free thyroxine and triiod othyronine are widely used diagnostic methods for thyroid function eva luation. However, some serum samples will demonstrate a nonspecific bi nding with assay reagents that can interfere with the measurement of t hese hormones. Several recent case reports have described the presence of such interferences resulting in reported abnormal concentrations o f thyroid hormones inconsistent with the patient's thyroid state. Circ ulating thyroid hormone autoantibodies, described in thyroid and nonth yroid disorders, are an important class of interference factor and can bind to hormone tracers used in various immunoassays. Two additional categories of interfering antibodies may particularly interfere within two-site immunoassays for thyrotropin. These include heterophile anti bodies, especially human anti-mouse antibodies, and rheumatoid factors , which can cause interferences by immunoglobulin aggregation and (or) cross-linking of both capture and signal antibodies. Here we review t he nature of these disturbances; their occurrence, prevalence, and det ection; and the clinical consequences of the failure to recognize such interference.