In 162 patients with end-stage renal disease (ESRD), 112 on maintenance haemodialysis (HD) and 50 on continuous ambulatory peritoneal dialysis (CAPD), thyroid status was evaluated: thyrotropin (TSH, IRMA, normal range 0.155 mU/l), total thyroxine (TT4, RIA, 70140 nmol/l), free thyroxine (FT4, RIA, 1125 pmol/l), total triiodothyronine (TT3, RIA, 13 nmol/l), free thyroxine (FT3, RIA, 2.55.8 pmol/l); in 113 patients (63+50) also reverse T3 (RT3, RIA, 0.140.54 nmol/l) was assayed. None of the patients had previously been treated for or suspected of a thyroid dysfunction.
Among HD patients, 11.6% had higher TSH, 38.4% lower TT4, 56.3% lower FT4, 21.4% lower TT3, 19.6% lower FT3, and 17.5% higher RT3 than the respective normal range. In CAPD patients, the corresponding values were 20, 8, 62, 16, 10, and 4%. There was a significant difference between HD and CAPD groups in TSH (medians 2.07 and 3.12, respectively, P<0.001, MannWhitney), in TT4 (77.5 and 107.3, P<0.001), in FT3 (3.17 and 3.82, P=0.019), and in RT3 (0.34 and 0.28, P=0.004). Both in HD and CAPD patients there were highly significant correlations (all P<0.001) between TT4 and FT4 (Spearman rho 0.658 and 0.674, in HD and CAPD respectively), and between TT4 and TT3 (0.355 and 0.526). Less expectedly, there were also strong correlations between TT4 and RT3 (0.605 and 0.695), and FT4 and RT3 (0.700 and 0.674).
Our data confirm the frequent deviations from normal values in ESRD patients, reflecting the complex alterations in thyroid hormone metabolism as well as assay-dependent variations. The pattern of non-thyroidal illness was more expressed in HD than in CAPD patients, including an increase in RT3, rarely observed in renal disorders. The close correlation between T4 and RT3 may theoretically reflect variations in deiodinase I activity among patients with kidney failure.