Alterations of thyroid hormone indices in acute renal failure and in acute critical illness with and without acute renal failure.

The present study evaluated thyroid hormone indices of patients with acute renal failure without other systemic illnesses (n = 12), as compared to patients with critical illnesses in the presence (n = 16) and absence (n = 6) of acute renal failure. Abnormalities in the group with acute renal failure alone included decreased serum levels of total T4 and T3, and elevated levels of free rT3. Serum levels of free T4 by equilibrium dialysis and the enzyme immunoassay, T3 uptake ratios, TSH and total rT3 were normal. These findings are consistent with the presence of decreased binding of T4 and rT3 to their serum carrier proteins. Critically ill patients with acute renal failure differed in that they had lower total T4 and T3 levels and elevated T3 uptake ratio values. As in the group with acute renal failure alone, total rT3 levels were normal and free rT3 values were elevated. The group with critical illness alone differed only in that the total rT3 concentrations were elevated in all patients. The alterations of thyroid hormone indices in acute renal failure are similar to those of other nonthyroidal illnesses with the exception of the normal total rT3 levels. This suggests that the failing kidney or the metabolic consequences of uremia specifically affect rT3 metabolism.