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Inder J. Chopra, Euthyroid Sick Syndrome: Is It a Misnomer?, The Journal of Clinical Endocrinology & Metabolism, Volume 82, Issue 2, 1 February 1997, Pages 329–334, https://doi.org/10.1210/jcem.82.2.3745
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THE TERM euthyroid sick syndrome (ESS) identifies abnormalities in thyroid function tests observed in patients with systemic nonthyroidal illnesses (NTIs) and those undergoing surgery or fasting (1, 2). The term nonthyroidal illness syndrome (NTIS) has also been employed to describe these abnormalities (3). These abnormalities result from variable, usually reversible, disturbances in the hypothalamo-pituitary-thyroid axis, thyroid hormone binding to serum proteins, tissue uptake of thyroid hormones, and/or thyroid hormone metabolism. Several recent reviews have addressed these issues (3–6). I shall focus mainly on the clinical diagnosis, significance, and treatment of ESS.
NTIS
Abnormalities of thyroid function in NTIS have been classified as 1) low T3 syndrome, 2) low T3-low T4 syndrome, 3) high T4 syndrome, and 4) other abnormalities (7).
Although serum concentrations of total T3 and T4 are now measured routinely by similar RIAs, several methods have been employed for measurement of the small, biologically active, free fraction of T3 and T4 (8–14). Most workers in the field view the measurement of free thyroid hormones by equilibrium dialysis as the gold standard, and the ultrafiltration method is comparable or a close second. Until recently, tracer equilibrium dialysis was believed to be the most accurate procedure for measurement of free T3 or T4. This is expected to be increasingly replaced by the newer, more accurate, equilibrium dialysis/RIA (12, 14); reasonably priced kits are available commercially for free T4 measurement by this procedure (Nichols Diagnostics, San Juan Capistrano, CA) and should be available soon for free T3 measurement. A detailed discussion of methods of measurement of free thyroid hormones is beyond the scope of this minireview, and the reader is referred to several studies comparing available procedures (9, 10, 13). The analog methods for free thyroid hormone measurements are popular in several countries outside of the United States. These methods yield free thyroid hormone readings in NTI that are similar to those from the index method and different from those by the tracer equilibrium dialysis or equilibrium dialysis/RIA procedures (9, 10, 13). For this review, I have relied mainly on free thyroid hormone levels measured by the newer equilibrium dialysis/RIA procedure when data are available, or those measured by tracer dialysis and/or ultrafiltration procedures.
