Thyroid Function in Renal Failure

Summary Renal failure is often associated with abnormal thyroid function tests which may make the diagnosis of thyroid dysfunction difficult (Table 1). As many as one‐half of patients with renal failure have low thyroid function indices. Although clinically the patients are usually euthroid, there is evidence from animal and human studies that there may be some degree of tissue hypothyroidism in patients with renal failure. Whether this tissue hypothyroidism reflects an adaptive reaction to the uremic state is not clear. Contributory factors to the alteration in thyroid function tests in renal failure are multiple and include poor nutritional status, medications, metabolic disturbances, hemodialysis, and associated nonthyroidal illnesses. All of these are known to affect thyroid function tests, and it is difficult to dissociate their influence from that of the uremic state. In most instances, the changes in thyroid function tests are similar to those encountered during nonthyroidal illness and include low levels of T 3 , with normal or low levels of T 4 , a variable free thyroxine index, and a normal, suppressed, or elevated level of TSH. One feature distinguishing renal failure from other non‐thyroidal illnesses is the often normal rT 3 and elevated free rT 3 levels seen in acute and chronic renal failure. This appears to be related to the increased binding of rT 3 to intracellular binding proteins. During hemodialysis, the free T 4 level is elevated transiently but may be abnormally elevated or low in the presence of a coexistent nonthyroidal illness. TSH is normal or only slightly elevated. Transplant patients, who often receive high doses of steroids, may have abnormal thyroid function tests, in particular hypothyroxinemia and suppressed levels of basal TSH.