title: A new serum cystatin C formula for estimating glomerular filtration rate in newborns.
abstract: BACKGROUND
  The levels of serum cystatin C (CysC) and creatinine (Cr) were determined in small-for-gestational-age (SGA) babies and compared with those for normal term newborns appropriate for gestational age (AGA), at birth and 3 days later. We then compared a number of cysC-based, Cr-based and combined formulas for estimation of glomerular filtration rate (GFR) with the neonatal reference GFR.
  
  
  METHODS
  Fifty full-term SGA and 50 AGA newborns were enrolled in the study. Kidney volume measurements were performed by ultrasound for each newborn.
  
  
  RESULTS
  At birth, the mean level of CysC in SGA babies was 1.48 ± 0.30 mg/l in cord blood and 1.38 ± 0.18 mg/l in day 3 blood samples, and the mean Cr level, determined simultaneously, was 67.08 ± 17.62 and 55.62 ± 14.91 μmol/l, respectively. These levels did not differ significantly from those determined in AGA babies. A 10 % reduction in kidney volume was associated with an increase in CysC value of 9.3 % in cord blood. The Cr-based and Schwartz-combined equations underestimated GFR relative to CysC-based and Zappitelli-based equations at birth and 3 days later.
  
  
  CONCLUSIONS
  A newly constructed Cys-C based formula which includes kidney volume and body surface area in the calculations for GFR is a reliable marker of GFR compared with neonatal reference clearance values.
authors.affiliation: Unit of Neonatology, Clinical Department of Gynecology and Perinatology, University Medical Center Maribor, Maribor, Slovenia, milena.treiber@ukc-mb.si.
authors.forename: Milena
authors.initials: M
authors.lastname: Treiber
authors.forename: Breda
authors.initials: B
authors.lastname: Pečovnik Balon
authors.forename: Maksimiljan
authors.initials: M
authors.lastname: Gorenjak
mesh_terms: D015415:Biomarkers / Q000097:blood; D001830:Body Surface Area; D015331:Cohort Studies; D003404:Creatinine / Q000097:blood; D003430:Cross-Sectional Studies; D055316:Cystatin C / Q000097:blood*; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007231:Infant, Newborn; D007236:Infant, Small for Gestational Age / Q000097:blood*; D007668:Kidney / Q000000981:diagnostic imaging*; D007677:Kidney Function Tests / Q000379:methods*; D008297:Male; D012016:Reference Values; D014463:Ultrasonography
chemical_list: D015415:Biomarkers; C525030:CST3 protein, human; D055316:Cystatin C; D003404:Creatinine