Martin l. Surks, MD; Inder J. Chopra, MD; Cary N. Mariash, MD; John T. Nicoloff, MD; David H. Solomon, MD

Selection of appropriate laboratory determinations will enable the clinician to diagnose thyroid dysfunction readily in the majority of patients. At the present time, estimation of free thyroxine and a "sensitive" thyrotropin assay are recommended as the principal laboratory tests for thyroid disease. A decrease in serum free thyroxine estimate and a raised level of serum thyrotropin confirm the diagnosis of hypothyroidism caused by thyroid gland failure. An increase in free thyroxine estimate combined with a serum sensitive thyrotropin level suppressed to less than 0.1 mU/L establishes the diagnosis of thyrotoxicosis. In sick patients, a normal or raised serum free thyroxine estimate together with a normal level of serum thyrotropin suggests that the patient has neither hypothyroidism nor thyrotoxicosis. Patients with severe illnesses, generally in the intensive care unit, and those treated with certain drugs, as well as individuals with unusual thyroid disorders, may present with confusing laboratory findings. An understanding of the regulation of the thyroid hormone system and/or judicious consultation with an endocrinologist should enable the clinician to diagnose thyroid disease, if present, in such patients. JAMA. 1990;263:1529-1532

CLINICAL investigations and commercial developments during the last decade have resulted in a large number of laboratory tests becoming available for diagnosis of thyroid dysfunction. To evaluate a patient for thyroid disease, the clinician must now select the most appropriate laboratory determinations from this bewildering array of tests. Many of these determinations have similar names and some lack diagnostic specificity. The American Thyroid Association has a continuing interest in clarifying and simplifying the nomenclature of these measurements; current guidelines for classification of tests and their nomenclature have been published recently.[1] The purpose of the present report is to suggest to clinicians an approach to the laboratory diagnosis of the principal thyroid disorders. In consideration of the low frequency of undiagnosed thyroid disease in the adult population,[2] the costs of various measurements, and the complexities in interpretation, our current view is that tests of thyroid function should not be part of multiphasic screening for patients who are not suspected to have thyroid disease, except in certain high- risk populations. Suspect populations include the newborn, for whom screening for congenital hypothyroidism is mandatory[3]; individuals with a strong family history of thyroid disease; elderly patients[4]; postpartum women 4 to 8 weeks after delivery, and patients with autoimmune diseases such as Addison's disease and type I diabetes mellitus. Rather, our premise is that clinicians will have a specific thyroid disease entity in mind when selection of tests is considered.