Correlations Of Serum Concentrations Of Cystatin C With Thyroid Function

Objective:The aim of the present study was to assess serum concentrations of Cys C in hyperthyroid and hypothyroid patients before and after treatment,and in hyperthyroid as well as hypothyroid rats that induced by drugs,to evaluate the role of potential determinants of serum Cys C levels in these subjects.Methods:Serum concentrations of Cys C were measured by an immunological turbidimetric assay in 36 hyperthyroid and 34 hypothyroid patients in the untreated state and again after restoration of euthyroidism,36 age- and sex-matched normal subjects served as controls,serum concentrations of free triiodothyronine(FT₃),free thyroxine (FT₄) and thyrotropic-stimulating hormone(TSH) were measured by an electrochemoluminescence immunoassay.Hyperthyroid(n=12) and hypothyroid(n=10) rats were separately induced by administration of levothyroxine and thiamazole,controls (n=10) were given 1 ml normal saline,the serum concentrations of Cys C of hyperthyroid,hypothyroid rats and controls were determined by ELISA before drug feeding(day 0) and after 1,3,7,10 days of drug feeding and 20 days after drug withdrawal.Results:Serum concentrations of Cys C were significantly higher(P＜0.001) and lower (P＜0.01) separately in hyperthyroid and hypothyroid patients than those in control group. After treatment,serum concentrations of Cys C were significantly decreased(P＜0.001) in hyperthyroid patients and significantly increased(P＜0.01) in hypothyroid patients, compared to normal control group,there was no significant difference(P＞0.05).Serum concentrations of Cys C showed significantly positive correlation with serum concentrations of FT₃(r=0.791,P＜0.001) and FT₄(r=0.796,P＜0.001),markedly negative correlation with serum concentrations of TSH(r=-0.511,P<0.001).Serum concentrations of were significantly higher on day 1 after administration of levothyroxine than control rats(P＜0.05),but Cys C levels on days of 3,7,10 after administration and 20 days after withdrawal of drugs had no significant difference from control rats(P＞0.05).The concentrations of Cys C on day 1 after administration were higher than those before administration(P＜0.05),but not on days of 3,7,10 after administration and 20 days after withdrawal of drugs(P＞0.05).Serum concentrations of Cys C in hypothyroid rats on days of 1,3,7,10 after administration of methimazole and 20 days after withdrawal of drugs had no significant difference from vehicle-treated control rats and those before administration(P＞0.05).Conclusions:Thyroid dysfunction has a major impact on human serum Cys C levels, change as the change of thyroid function status:serum Cys C levels are higher in the hyperthyroid and lower in the hypothyroid state as compared with the euthyroid state. Levothyroxine can increase serum Cys C levels temporarily,but thiamazole has no effect on it.Serum FT₃,FT₄ and/or TSH may have a regulatory role in the production and secretion of Cys C from all nucleated cells.We recommend that altered thyroid function should be considered when CysC is determined clinically.