Cystatin C and creatinine after successful kidney transplantation in children

BACKGROUND: Serum creatinine is commonly used for the monitoring of allograft function following renal transplantation (RTX). Due to lower muscle mass, creatinine production rate is reduced in children, thus decreasing its sensitivity for the detection of allograft dysfunction. In children, the serum concentration of cystatin C, a low molecular weight protein of 13.3 kDa, reflects glomerular filtration rate independent of age, height and body composition. We, therefore, sought to assess the potential of cystatin C as a marker of allograft function in children. METHODS: Cystatin C and creatinine were measured in parallel at least daily in 24 children (14 boys, 10 girls; mean age 10.5+/-5.1 years) during hospitalization after successful RTX. Cystatin was determined immunoturbidimetrically, creatinine enzymatically. RESULTS: Within one hour after RTX, cystatin C (mean+/-SE) almost halved from 6.69+/-0.45 mg/l to 3.69+/-0.38 mg/l while creatinine declined from 862 +/-65.4 to 633+/-62.9 micromol/l. Following a nadir of 1.82+/-0.18 mg/l on day 2, there was a secondary increase in cystatin C concentrations to 2.69+/-0.35 mg/l on day 10. Creatinine concentrations continued to decline until day 9 reaching 80.5+/-13.1 micromol/l. Day-to-day variation at steady-state was comparable. In the course of 9 acute rejection episodes, both parameters rose in parallel, the increase in creatinine concentration being much greater. CONCLUSION: Cystatin C was an early indicator of allograft function following successful RTX in children. It did not prove superior to creatinine for the recognition of acute allograft dysfunction, however.