Impact of thyroid function on serum cystatin C and estimated glomerular filtration rate: a cross-sectional study.

OBJECTIVE: To determine the relationship between thyroid-stimulating hormone (TSH) and cystatin C (CysC) and estimated glomerular filtration rate calculated by Cys C (eGFR(CysC)).

METHODS: We conducted a cross-sectional study including 8,126 male participants. Serum creatinine (Cr), CysC, eGFR calculated by Cr (eGFR(Cr)), and eGFR(CysC) were determined and compared in euthyroid and subclinical thyroid dysfunction patients. Relationships between TSH and Cr, cystatin C, eGFR(Cr), and eGFR(CysC) were assessed by linear and quadratic trend analyses. Odds ratios (ORs) of chronic kidney disease (CKD; eGFR<60 mL/min/1.73 m2) were calculated according to categories of thyroid function using TSH values of 2.01-3.00 mIU/L as a reference.

RESULTS: Serum CysC level was significantly elevated, and eGFR(CysC) was significantly reduced in both subclinical hypothyroidism and subclinical hyperthyroidism. TSH was negatively and linearly associated with Cr and eGFR(Cr) (P<.001). Quadratic trends were found between TSH and cystatin C or eGFR(CysC) (P<.001). Compared with individuals with TSH of 2.01-3.00 mIU/L, the prevalence of CKD(CysC) was significantly higher in subjects with TSH<0.40 mIU/L, 3.01-4.00 mIU/L, and 4.01-7.00 mIU/L, while the prevalence of CKD(Cr) was only significantly higher in subjects with TSH>7.0 mIU/L.

CONCLUSIONS: Despite only studying male subjects and using eGFR rather than standard GFR, we conclude that thyroid function differentially affects serum CysC and Cr concentrations. Subclinical hypothyroidism and subclinical hyperthyroidism are both associated with elevated CysC, reduced eGFR(CysC), and higher prevalence of CKDCysC. Assessment of renal function with CysC should be avoided in patients with thyroid dysfunction.