Nozawa et al.19 compared Cin with eGFR using the serum creatinine (eGFRcreat), eGFR using the serum cystatin C concentration (eGFRcys), the mean of eGFRcreat, eGFRcys (eGFRavg) and endogenous 24-h creatinine clearance × 0.715 (Ccr × 0.715) in 30 RA patients with a daily prednisolone dose less than 10 mg and demonstrated that eGFRcys was correlated best with Cin, and that the relationship was close to y = x. This evidence concerns the gene CST3 and rheumatoid arthritis.