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Section 1.
Forward and Introduction


Physicians need quality laboratory support for the accurate diagnosis and cost-effective management of thyroid disorders. Sometimes the clinical suspicion is strong, as in obvious hyperthyroidism in a young adult or a rapidly growing thyroid mass, and laboratory support simply confirms the suspicion. However in the majority of patients, symptoms may be subtle so that only biochemical testing or cytopathologic evaluation can detect the disorder. However overt or obscure a patient's thyroid problem, an open collaboration between physicians and clinical biochemists is essential for optimal, cost-effective care.

Since the first publication of this monograph in 1996, a number of professional organizations have published standards of care guidelines for using thyroid tests. Because geographical and economic factors impact the clinical use of thyroid tests to some extent, this revised monograph will focus on the technical aspects of thyroid tests and the performance criteria needed for optimal clinical utility in an increasingly cost-sensitive global environment. This monograph is designed to give both clinical biochemists and physicians an overview of the current strengths and limitations of the thyroid tests most commonly used in clinical practice.


A. Additional Resources

Current clinical guidelines are published in the following references (1-3). In addition, the textbooks "Thyroid" and "The Thyroid and Its Diseases" ( are useful references (4, 5). A list of symptoms suggesting the presence of thyroid disease together with the ICD-9 codes recommended to Medicare by the American Thyroid Association is available on the organization's website ( Clinical practice guidelines may vary, depending on region. More information can be obtained from each of the thyroid organizations: Asia & Oceania Thyroid Association (AOTA = www; American Thyroid Association (ATA =; European Thyroid Association (ETA = ) and Latin American Thyroid Society (LATS =


B. Historical Introduction

Over the past forty years, improvements in the sensitivity and specificity of biochemical thyroid tests, as well as the development of fine needle aspiration biopsy (FNAB) and improved cytology techniques, have dramatically impacted clinical strategies for detecting and treating thyroid disorders. In the 1950s, only one serum-based thyroid test was available - an indirect estimate of the total (free + protein-bound) thyroxine (T4) concentration, using the protein bound iodine (PBI) technique. Today, urine iodine concentrations, measured by dry or wet-ash techniques, are used to estimate dietary iodine intake and output. The development of radioimmunoassays (RIA) in the early 1970s and more recently, non-isotopic immunometric assay (IMA) methods have progressively improved the specificity and sensitivity of thyroid hormone testing. Currently, serum-based tests are available for measuring the concentration of both total (TT4 and TT3) and free (FT4 and FT3) thyroid hormones in the circulation (6). In addition, measurements of the thyroid hormone binding plasma proteins, Thyroxine Binding globulin (TBG), Transthyretin (TTR)/Prealbumin (TBPA) and Albumin are available. Improvements in the sensitivity of assays to measure the pituitary thyroid stimulating hormone, thyrotropin (TSH) now allow TSH to be used for detecting both hyper- and hypothyroidism. Further, the measurement of the thyroid hormone precursor protein, Thyroglobulin (Tg) in serum has become an important tumor marker for managing patients with differentiated thyroid carcinomas. The recognition that autoimmunity is a major cause of thyroid dysfunction has led to the development of more sensitive and specific tests for autoantibodies to thyroid peroxidase (TPOAb), thyroglobulin (TgAb) and the TSH receptor (TRAb).

Current thyroid tests are usually performed on serum by either manual or automated methods that employ specific antibodies. Methodology is still evolving as performance standards are established and new technology and instrumentation are developed.


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