Laboratory medicine practice guidelines: laboratory support for the diagnosis and monitoring of thyroid disease

Quality thyroid tests are essential for diagnosing and managing thyroid conditions. Indeed, mild (subclinical) hypoand hyperthyroidism are by definition conditions that are recognized by their biochemical profile, typified by an abnormal serum TSH concentration associated with normal range free thyroid hormone (FT4 and FT3) levels. The National Academy of Clinical Biochemistry (NACB) has recently published a consensus monograph entitled Laboratory Medicine Practice Guidelines: Laboratory Support for the Diagnosis and Monitoring of Thyroid Disease that reviews the clinical utility and technical performance of current thyroid tests (Demers & Spencer, 2002). The current scientific literature abounds with articles relating to thyroid conditions, strategies for thyroid testing and the technical performance of different thyroid methodologies. This monograph was prompted by the need to develop a consensus concerning these issues as well as to address the unusual thyroid problems that challenge the diagnostic accuracy of the thyroid tests currently available. These atypical presentations account for a disproportionately large expenditure of laboratory resources to determine the correct diagnosis (Kricka, 2000). In ambulatory patients these unusual presentations include: binding protein abnormalities that affect the diagnostic accuracy of FT4 tests; the presence of thyroglobulin (Tg) autoantibodies that interfere with serum Tg measurements; and medications that compromise the in vivo and in vitro metabolism of thyroid hormones and influence the diagnostic accuracy of TSH measurements. In addition, severe forms of non-thyroidal illnesses (NTI) have a myriad of effects on thyroid test results. This monograph is unique because it contains consensus guidelines that were developed by a process of global review. The review process was initiated at the International Thyroid Congress in Kyoto in October 2000, after which the guidelines were displayed electronically in addition to being distributed to more than 100 thyroid specialists, representing diverse professional associations worldwide, for consensus-building. The information contained in the monograph is presented in discrete chapters. Each chapter covers the clinical utility of a specific test, and contains focused guidelines that describe the physiological strengths and limitations of the test together with its optimal technical performance parameters. Most of the guidelines appeared to have greater than 95% consensus; however, there were some geographically sensitive differences in practice patterns.