Cystatin C Serum Concentrations Underestimate Glomerular Filtration Rate in Renal Transplant Recipients

Abstract

Cystatin C, a cationic 13.3-kDa protein (1) has recently been described as a promising endogenous marker of glomerular filtration rate (GFR) (2) in both adults (2)(3) and children (4)(5). Correlation of serum cystatin C concentrations with the results of inulin and 51Cr-ethylenediaminetetraacetic acid clearance examinations was superior to serum creatinine (2)(3)(4). Although patients with a wide range of renal function were examined, the potential effect of underlying disease on this correlation has not been studied yet. In a recent longitudinal study on 24 pediatric renal transplant recipients, cystatin C serum concentrations were found to underestimate GFR compared with the results of a 24-h creatinine clearance (6). To validate these findings, we extended our previous study on the correlation between inulin clearance (CIn) and serum cystatin C concentration in children (4). One hundred and eighty-four children (87 girls, 97 boys) with a mean age of 11.2 ± 4.5 years (mean ± SD; range, 0.24–17.96 years) had undergone an inulin clearance examination between 1985 and 1995 at the Department of Pediatric Nephrology at Hannover Medical School. Forty-four of these (19 boys, 25 girls; mean age, 13.9 ± 3.2 years) had received a renal transplantation (RTx). Serum samples from CIn examinations had been stored at −20 °C for 6.9 ± 2.8 years (mean ± SD) until measurement of cystatin C, which has been shown to be stable for such extended periods of storage (4). Cystatin C was measured by particle-enhanced immunoturbidimetry (2)(3) using the Cystatin C PET-Kit (Dako) on a Hitachi 717 automated analyzer (Roche Diagnostics). Because the GFR was subnormal in all of the RTx recipients, this group was compared with a control group of 56 non-RTx children (26 boys, 30 girls; mean age, 11.2 ± 4.8 …