Thyroid functions before and after maintenance hemodialysis in patients with chronic renal failure

To study the factors involved in the low thyroid hormone levels in patients with chronic renal failure (CRF), we investigated thyroid functions just before and after hemodialyses (HD) in 32 such patients who were on maintenance HD. In addition, we measured serum thyroid hormone binding inhibitor activities (THBI) in another set of 37 patients. None of the patients had been suspected of having thyroid diseases. HD duration and aging did not have a significant effect on the results of the thyroid function tests. Before each HD, the serum concentrations of T3, T4, FT3, FT4, rT3, PBI, FT3I, FT4I, FT3/T3, FT4/T4, T4/TBG, T4/TSH and FT4/TSH were lower, and those of TSH, TBG, and thyroglobulin (Tg) were higher in the patients than in normal controls. The thyroid hormone concentrations were negatively correlated with the BUN and creatinine levels. The Tg levels were positively correlated with the BUN levels. After each HD, almost all the thyroid function tests including T4/TBG ratio showed improvements, which indicated that hemodilution and a decrease in the T4-binding affinity of TBG with thyroid hormones were the major factors in the low thyroid hormone levels in CRF patients. However, even after HD, T3, FT3, rT3, T4/TSH and FT4/TSH were still lower and TSH and Tg were still higher in the patients. These data suggested that the CRF patients were in a subclinical hypothyroid state. THBI was high in patients with CRF and did not change following HD. NEFA did not seem to contribute to the high THBI before HD, because they were in the normal range. However, as NEFA became very high after HD and possessed THBI, we calculated the corrected THBI (C-THBI) by subtracting the effect of NEFA from total THBI. C-THBI was high before HD and decreased after HD. Therefore, it was suggested that this C-THBI contributed to the abnormalities in the affinity of TBG with thyroid hormones. From these studies, it is concluded that (1) the patients with CRF may be in a subclinical hypothyroid state, although hemodilution was seen to have a strong effect on the thyroid hormone concentrations, and (2) C-THBI may have an effect on the affinity of TBG with thyroid hormones and play an additional role in low thyroid hormone levels in these patients. The mechanisms of hypothyroidism and the nature of C-THBI remain to be clarified.