Thyroid function and lipids in patients with chronic renal disease treated by hemodialysis: with comments on the "free thyroxine index".

It is known that hypertriglyceridemia and abnormal thyroid function tests are common in patients with chronic renal disease treated by hemodialysis, but a possible association between these abnormalities has not been investigated. We measured serum thyroid hormone and lipid levels in one hundred patients receiving chronic hemodialysis. There were ten patients with elevations in serum thyrotropin (TSH). In the remaining patients with normal TSH, those receiving no drugs known to affect thyroid function had low mean values for thyroxine (T₄) and triiodothyronine (T₃), while the mean T₃ resin uptake (fraction of T₃ bound to resin, T₃U) was normal, resulting in low mean values for free T₄ index (FT₄I = T₄ × T₃U) and free T₃ index (FT₃I = T₃ × T₃U). The depression in T₃ was greater than the depression in T₄, so that $\text{T}{}_3\text{T}{}_4$ ratios were also low. Androgen-treated male patients had the lowest T₃ and T₄ levels; their T₃Us were high, presumably reflecting androgen-induced depression of T₄-binding globulin, but their mean FT₄I and FT₃I were still lower than those of the other patients. Evidence is presented that the conventional T₃U underestimates the proportion of free hormone when binding protein levels are low, and that a “new T₃U,” the ratio of resin-bound T₃ to serum protein-bound T₃, more accurately reflects the proportion of free hormone. Computing a “new FT₄I,” as new T₃U × T₄, yielded values in the androgen-treated group similar to those of the other patients. Patients receiving propranolol had lower $\text{T}{}_3\text{T}{}_4$ ratios than the other patients, presumably due to propranolol's inhibitory effect on peripheral conversion of T₄ to T₃. No relationship was found between indexes of thyroid function and lipid levels. Subjects with high TSH levels had levels of triglyceride and cholesterol similar to the remaining patients. Among those with normal TSH levels, low levels of T₃ or T₄ did not correlate with abnormal lipid levels. It is concluded that thyroid hormone abnormalities do not explain the hypertriglyceridemia of patients on chronic hemodialysis. The frequency of low T₄ and T₃ values in such patients, in the absence of clinical evidence of hypothyroidism and, in most instances, in the absence of TSH hypersecretion, remains unexplained.