Reference ranges for plasma cystatin C and creatinine measurements in premature infants, neonates, and older children

Aim-To establish a reference range in the paediatric population for the new glomerular filtration rate (GFR) marker, cystatin C, and to compare it with that of creatinine. Methods-Cystatin C and creatinine were measured by particle enhanced nephelometric immunoassay (PENIA) and fixed interval Jaffe methods, respectively, in 291 children aged 1 day to 17 years, including 30 premature infants with gestational ages ranging from 24 to 36 weeks. Results-In the premature infants, concentrations of both cystatin C and creatinine were significantly raised compared with term infants, with cystatin C concentrations being between 1.10 and 2.06 mg/litre and creatinine between 32 and 135 mu mol/litre. In premature infants, there was no significant relation between gestational age and cystatin C or creatinine concentration. Creatinine concentrations fell to a nadir at 4 months of age, rising gradually to adult values by about 15-17 years of age, in contrast to cystatin C, which fell to a mean concentration of 0.80 mg/litre by the Ist year of life, and remained constant throughout adulthood up to the age of 50 years. Neither analyte showed any influence of sex. Conclusion-The measurement of cystatin C, rather than creatinine, is more practical for monitoring GFR changes in the paediatric population.