![]() ![]() ![]() This is the role of type 1 and 2 iodothyronine deiodinases (D1 and D2). When dietary iodine is sufficient, the major product of the thyroid gland is thyroxine (T4) which is secreted at a rate of 10-fold that of 3,5,3′-triiodothyronine (T3) in humans.īut a rate-limiting step in thyroid hormone action is the conversion of the prohormone T4 to T3. T3 is more active than T4 and is the final form of the hormone, though it is present in less quantity than T4. In peripheric tissues T4 is converted as required by iodothyronine deiodinase. Thyroid hormones (T4 and T3) are produced by the follicular cells of the thyroid gland and are regulated by TSH made by the thyrotropes of the anterior pituitary gland. They are often associated with alterations in other endocrine axes, in particular reduction in serum gonadotropin and sex hormone concentrations and increase in serum free cortisol levels. This changes in parameters of thyroid function are rarely isolated. In patients with no previous diagnosis of thyroid disease, critical illness (defined as a life-threatening condition) can cause profound changes in thyroid hormone metabolism.Ĭauses of euthyroid sick syndrome include a number of acute and chronic conditions, including pneumonia, fasting, starvation, anorexia nervosa, sepsis, trauma, cardiopulmonary bypass, malignancy, stress, heart failure, hypothermia, myocardial infarction, chronic renal failure, cirrhosis and diabetic ketoacidosis.Įuthyroid sick syndrome affects up to 70% of patients hospitalized with diseases of various etiologies, especially in ICUs. ![]() After recovery from an NTI, these thyroid function test result abnormalities should be completely reversible. As the severity increases, both serum T3 and T4 levels drop and gradually normalize as the patient recovers. The most prominent alterations are low serum triiodothyronine (T3) and elevated reverse T3 (rT3), leading to the general term "low T3 syndrome." Thyroid-stimulating hormone (TSH), thyroxine (T4), free T4 (FT4), and free T4 index (FTI) also are affected in variable degrees based on the severity and duration of the non-thyroidal illness. Such changes may be a self-protective adaptation to illness, as the body attempts to conserve energy. T3 is the biologically active thyroid hormone and its low serum levels in critical illness reflect altered thyroid homeostasis and a mechanism of adaptation. The fact that the syndrome is not caused by an intrinsic abnormality in thyroid function has lead to the definition of “Non-Thyroidal Illness Syndrome”. The most common abnormality results in low T3 thyroid hormone with progressive decrease in thyroxine (T4) and TSH. Euthyroid Sick Syndrome (or Low T3 Syndrome or Non-Thyroidal Illness Syndrome) is a condition of abnormal thyroid hormones release in patients with apparently normal thyroid gland during severe systemic illness, physical trauma, and psychiatric disturbances. ![]()
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