Serum reverse triiodothyronine (3,3',5'-L-triiodothyronine) in chronic renal failure.

Serum reverse triiodothyronine (reverse T3), triiodothyronine (T3), thyroxine (T4) and thyrotropin (TSH) concentrations were determined by radioimmunoassay in end-stage chronic renal failure, hypothyroidism and control subjects. In advanced chronic renal failure serum reverse T3 was normal or elevated and serum T3 concentrations were frequently, and serum T4 occasionally, lowered. Serum TSH was normal even where serum T3 and T4 concentrations were low. Normal or elevated serum reverse T3 associated with normal serum TSH in chronic renal failure clearly differentiates this disease from primary hypothyroidism in which low serum reverse T3 and high serum TSH are constantly found.