Paradoxical effects of thyroid function on glomerular filtration rate estimated from serum creatinine or standardized cystatin C in patients with Japanese Graves' disease

Background: Estimated glomerular filtration rate (eGFR) is clinically valuable for evaluating renal function. Recently, serum cystatin C (sCysC) measurement has been standardized and has demonstrated utility as a novel indicator of renal function. Thyroid hormone is known to affect serum creatinine (sCr) and sCysC, however, the clinical significance of post-treatment renal function evaluation is yet to be completely elucidated. This study examined the effects of thyroid hormones on eGFR by sCr (eGFR(cr)), and standardized sCysC (eGFR(cysc)) in patients with Japanese Graves' disease (GD). Methods: Serum samples were obtained from 113 outpatients with GD. Following pharmacotherapy, 41 of the 113 outpatients with GD achieved remission. Renal function was evaluated by eGFR(cr) and eGFR(cysc). Reference method used Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations. Results: eGFRa(cr) levels significantly increased whereas eGFR(cysc) levels significantly decreased with elevated FT3 and FT4 levels in patients with GD. In the remission group, eGFR(cr) levels significantly decreased and eGFR(cysc) levels significantly increased. No significant differences between eGFR(cr) and eGFR(cysc) levels were observed. Furthermore, CKD-EPI equations show a similar trend and eGFR(cr-cysc) levels were no significant differences regardless of before and after treatment. Conclusions: Renal function evaluation by eGFR(cr) and eGFR(cysc) had clinical utility in post-treatment euthyroidism. (C) 2015 Elsevier B.V. All rights reserved.