The examination and understanding of thyroid function perturbations in the intensive care unit (ICU) setting is often difficult, because the changes reflect apparent alterations in the ability to measure thyroid hormone parameters and homeostatic modulations in thyroid hormone metabolism accurately. Present concepts suggest that patients in the ICU setting are catabolic and that decreased extrathyroidal conversion of T4 to T3 decreases unnecessary energy expenditure. These alterations in thyroid function in a euthyroid, systemically ill patient are referred to as the euthyroid sick syndrome.<sup>8 Burman K.D. Current and potential endocrine therapeutics in critical illness Williams and Wilkens, Principles and Practice of Endocrinology and Metabolism Philadelphia: Lippincott (2000). 

Cliccare qui per andare alla sezione Riferimenti, 9 Burman K.D. Recent developments in thyroid hormone mtabolism: Interpretation and significance of measurements of reverse T3, 3, 3′–T2, and thyroglobulin Metabolism 1978 ;  27 : 615-630  [cross-ref]

Cliccare qui per andare alla sezione Riferimenti, 10 Burman K.D., Dimond R.C., Harvey G.S. , e al. Glucose modulation of alterations in serum iodothyronine concentrations induced by fasting Metabolism 1979 ;  28 : 291-299  [cross-ref]

Cliccare qui per andare alla sezione Riferimenti, 18 DeGroot L.J. Dangerous dogmas in medicine: The nonthyroidal illness syndrome J Clin Endocrinol Metab 1999 ;  84 : 151-164  [cross-ref]

Cliccare qui per andare alla sezione Riferimenti, 49 Wartofsky L. The low T3 or sick euthyroid syndrome: Update 1994 Endocrine Rev 1994 ;  3 : 248-251

Cliccare qui per andare alla sezione Riferimenti, 50 Wartofsky L., Burman K.D. Alterations in thyroid function in patients with systemic illness: The euthyroid sick syndrome Endocrine Rev 1994 ;  3 : 210-247

Cliccare qui per andare alla sezione Riferimenti, 51 Wartofsky L., Burman K.D. Alterations in thyroid function in patients with systemic illness: The “euthyroid sick syndrome.” Endocrine Rev 1982 ;  3 : 164-217  [cross-ref]

Cliccare qui per andare alla sezione Riferimenti, 52 Wartofsky L., Burman K.D., Dimond R.C. , e al. Studies on the nature of thyroidal suppression during acute falciparum malaria: Integrity of pituitary response to TRH and alterations in serum T3 and reverse T3 J Clin Endocrinol Metab 1977 ;  44 : 85

Cliccare qui per andare alla sezione Riferimenti, 53 Wartofsky L., Burman K.D., Ringel M.D. Trading one “dangerous dogma” for another? Thyroid hormone treatment of the “euthyroid sick syndrome.” J Clin Endocrinol Metab 1999 ;  84 : 1759-1760

Cliccare qui per andare alla sezione Riferimenti</sup> There are selected patients in the ICU who actually have biochemically perturbed thyroid function, either hypothyroidism or hyperthyroidism, in addition to the typical changes of the euthyroid sick syndrome. It is usually difficult to discern these patients from the larger population of euthyroid patients, partly because the usual clinical manifestations of hyper- or hypothyroidism overlap with the signs and symptoms of euthyroid patients who have altered results of thyroid function tests. Further, there is no absolute gold standard clinical or biochemical measurement that can be used to differentiate these two groups of patients. The purposes of the present article are to review the typical thyroid hormone alterations in the euthyroid sick syndrome and to discuss methods of differentiating this syndrome from pathologic thyroid dysfunction that requires specific thyroid therapy. The purpose of assessing thyroid function in a given patient is to assess the systemic metabolic action of thyroid hormones at the cellular level. Indeed, serum thyroid hormone measurements, no matter how accurate, may not be proportional to thyroid hormone action at the cellular level.

Sensitive thyrotrophin (third generation) assays that are capable of detecting .01 μU/mL of thyroid stimulating hormone (TSH) have been extremely helpful in this setting and have largely supplanted the need for performing a thyrotrophin releasing hormone (TRH) test.<sup>43 Spencer C.A., Takeuchi M., Kazarosyan M. Current status and performance goals for serum thyrotropin (TSH) assays Clin Chem: 1996 ;  42 : 164-173

Cliccare qui per andare alla sezione Riferimenti, 44 Spencer C.A., Takeuchi M., Kazarosyan M. , e al. Interlaboratory/intermethod differences in functional sensitivity of immunometric assays of thyrotropin (TSH) and impact on reliability of measurement of subnormal concentrations of TSH Clin Chem 1995 ;  41 : 367-374

Cliccare qui per andare alla sezione Riferimenti</sup> Assuming a normal pituitary gland, a serum TSH measurement in an ambulatory (noncritically ill) patient is the best measure of thyroid hormone action at the cellular level; an elevated TSH concentration shows hypothyroidism and a decreased or undetectable TSH level demonstrates hyperthyroidism. In patients in the ICU, these general principles apply, albeit with several important caveats that are discussed farther on.