Influence of glucocorticoid therapy on cystatin C based estimated glomerular filtration rate and classification of chronic kidney disease

Abstract

Background: The accurate assessment of renal function is essential for implementing safe therapy among patients with autoimmune diseases. Serum cystatin C（Cys）is less affected by muscle mass. However, factors that affect the serum level of Cys were not fully known. There were various opinions about the effect of glucocorticoid（GC）therapy to serum cystatin C concentration. In this study, we investigated the influence of GC to Cys based eGFR（eGFRcys）and compared chronic kidney disease status using eGFRcreat and eGFRcys.

Methods: This was an observational study in an outpatient rheumatology clinic of a single hospital. The consecutive patients had their serum Cr and Cys measured. The eGFRs were calculated using Cr and Cys（eGFRcreat and eGFRcys）. Patients were divided according to with or without oral GC therapy.

Results: In all, 189 patients（75.1% female）with various autoimmune diseases were included in the study. Their mean（SD）age was 68.3 years old（13.03）. The number of patients taking GC was 124（65.6%）. The mean dosage of GC of 124 patients was 4.6（SD3.18）mg/day of prednisolone. Mean eGFRcys was significantly lower than the mean eGFRcreat. The correlation coefficient between eGFRcreat and eGFRcys was 0.681 in 189 patients. There was no significant difference between the correlation coefficient of patients taking GC and that of patients not taking GC（0.73 vs. 0.62）. 38.6% of patients’ CKD status was discordant. Reclassification by eGFRcys was more likely in elderly patients and those with hypoalbuminemia.

Conclusions: We have observed the influence of small dosage of oral GC on eGFRcys. There are discrepancies in CKD status between eGFRcreat and eGFRcys. eGFRcys might be a good marker of renal function to predict the dose of renally excreted drugs.