Assay of Thyroid Hormones and Related Substances

Review
In: Endotext [Internet]. South Dartmouth (MA): MDText.com, Inc.; 2000.
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Excerpt

This chapter reviews how improvements in sensitivity and specificity of thyroid function tests [total and free thyroid hormones, TSH, thyroid autoantibodies (TRAb, TPOAb and TgAb) and thyroglobulin (Tg)] have dramatically improved clinical strategies for detecting and treating thyroid disorders. The review discusses the strengths and limitations of the different methodologies currently used (RIA, IMA and LC-MS/MS) and their propensity for analyte-specific interferences caused by heterogeneity (TSH, TgAb and Tg) or analyte-specific autoantibodies (T4Ab, T3Ab, TSHAb and TgAb). In addition, non-analyte related interferences from heterophile antibodies, including human anti-mouse antibodies (HAMA) and Rheumatoid Factor (RF), and interferences related to the use of Biotin and Streptavidin reagents, are discussed. The review provides an update on collaborations between the International Federation of Clinical Chemistry (IFCC) committee for the standardization of thyroid function tests (C-STFT) and the in-vitro diagnostic (IVD) industry- the goal being to eliminate between-method biases. Although re-standardization of thyroid hormone tests against established reference measurement procedures, and harmonization of TSH tests to the all-method mean has proved effective, recalibration has yet to be implemented by the IVD. Until between-method biases are eliminated, it is not feasible to propose universal reference ranges that would apply across methods. The review contains a comprehensive discussion of the clinical utility of Tg methodology (RIA, IMA or LC-MS/MS), used to monitor patients with differentiated thyroid cancer (DTC). Mechanisms for in-vitro and possible in-vivo TgAb interference with Tg testing are proposed. The methodologic and clinical strengths and weakness of each test are discussed relative to current guidelines.For complete coverage of this and related areas in Endocrinolofy, visit our free web-books, www.endotext.org and www.thyroidmanager.org.

Publication types

  • Review