One such explanation for the abnormal findings in the syndrome involve the  Thyroid Rescue 911 Review distinction between type 1 deiodinase and type 2 deiodinase enzymes. Type 1 deiodinase is usually found in the periphery while type 2 deiodinase is found mainly in the pituitary gland. In this particular condition, it is the activity of type 1 deiodinase which is decreased, resulting in less conversion of thyroxine to triiodothyronine.Despite all this, the type 2 deiodinase is not as affected as the type 1 deiodinase and the pituitary gland continues to sense normal levels of triiodothyronine. Because of this, the pituitary gland will inhibit the secretion of TSH due to what it perceives as normal concentrations of triiodothyronine. However, other factors should be considered and this theory does not account for the low levels of thyroxine as well.

Another explanation suggests that the serum thyroid hormone abnormalities may be due to inhibition of hormone-binding proteins, which consequently prevents test from reflecting normal free hormone levels. This binding inhibitor can be found in both serum and tissues and could inhibit binding to nuclear triiodothyronine receptors or prevent uptake of the thyroid hormones by the cells of the body. However, some studies have failed to exhibit such a binding inhibitor.Although patients with the sick euthyroid syndrome may exhibit signs of hypothyroidism such as hypothermia and a sluggish sensorium, they are not hypothyroid and should not receive thyroid hormone replacement as treatment. Treatment of such patients with thyroid hormone may, in fact, yield either no improvement or a worse outcome.
 

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