Hemodilution Impacts Assessment of Thyroid Status before and after Hemodialysis in Patients with End-Stage Renal Disease

Background: To elucidate the role of hemodilution in the alteration of thyroid hormone levels in end-stage renal disease (ESRD), we compared thyroid function before and after hemodialysis (HD). Methods: Twenty-three male ESRD patients (age <65 years) with either chronic glomerulonephritis (CGN) or diabetic nephropathy (DN), who were enrolled between June 2019 and August 2019, were included in the study. The free thyroxine (fT 4 ), free tri-iodothyronine (fT 3 ), and thyroid-stimulating hormone (TSH), thyroxine-binding globulin (TBG), and thyroglobulin (Tg), measured before and after HD in 12 patients with CGN (48.7 ± 11.8 years [mean ± standard deviation]) and 11 patients with DN (57.6 ± 6.5 years), were compared with 45 healthy controls (52.5 ± 11.9 years). Results: The fT 4 , fT 3 , and TBG were significantly low before HD and increased in parallel with an increase in hematocrit and albumin after HD in both ESRD subgroups. The TSH was high before HD and decreased significantly after HD, while Tg remained almost unchanged. In DN, the fT 4 levels were nearly identical, while fT 3 was lower with slightly higher TSH, compared with CGN. The TSH/fT 4 ratios before HD were significantly higher in both subgroups, and the fT 3 /fT 4 ratios after HD were significantly lower in DN than the control. Conclusions: Our findings suggest that the low fT 4 and fT 3 levels found in ESRD are due to hemodilution before HD, resulting in a slightly higher TSH level but almost unchanged Tg level, and that DN is associated with decreased T 4 -to-T 3 conversion.