Most investigators believe that persons with abnormal thyroid function test results during episodes of nonthyroidal illness are clinically euthyroid.1 However, the "true" thyroid status during illness is not known because independent assessment is not available (ie, basal metabolic rate, reflex relaxation time, systolic ejection time, and specific liver enzymes are either impractical in clinical application or nonspecific in the presence of other severe medical illness). Thus, we specifically avoided the concept of "true" thyroid status. Given these limitations, it remains important to differentiate persons with diagnosable, nontransient, thyroid illness from the transient state of thyroid hormone alterations in critical illness. We therefore wished to examine several methods of free T4 measurement to determine if the additional information obtained clarified the data available from routine thyroid function tests such as the T4, triiodothyronine resin uptake (T3RU), and thyroid-stimulating hormone (TSH).Our data indicated that little additional
Slag MF, Morley JE, Shafer RB. Evaluation of Thyroid Status-Reply. JAMA. 1982;247(16):2231–2232. doi:10.1001/jama.1982.03320410017011
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