Background. The aim of this study was to clarify the reference values of serum cystatin C
(cysC) as a marker of glomerular filtration rate (GFR) in full-term newborns, appropriate and
small for gestational age (SFD), and in neonates after perinatal hypoxia/asphyxia (AS) in
comparison with creatinine (Cr), Schwartz's formula and 3 different cystatin-C based
equations.
Patients and methods. 150 full-term newborns were enrolled, comprised of 3 groups (AS,
SFD and control). CysC and Cr were measured in serum samples from the umbilical cord at
birth (cysC-umb and Cr-umb) and from a peripheral vein 3 days later (cysC-3 and Cr-3).
Kidney volume measurements by ultrasound were made.
Results. At birth, the mean level of cysC in normal term babies was found to be 1.39 ± 0.19
mg/l, in AS group 2.12 ± 0.53 mg/l and in SFD group 1.48 ± 0.30 mg/l; not significantly
decreased in controls but in SFD and AS group after 3 days of life. Cr levels, determined
simultaneously at birth were 62.74 ± 12.84 μmol/l in control, 72.60 ± 15.55 μmol/l in AS and
67.08 ± 17.62 μmol/l in SFD group. After 3 days Cr levels significantly decreased in all three
groups. The ROC curve analysis, comparing AS versus control, showed AUC for cysC-umb,
cysC-3, Cr-umb and Cr-3 (0.918; 0.698; 0.692; 0.660). The highest diagnostic accuracy was
achieved with a chosen cut-off for cysC-umb of 1.67 mg/l (sensitivity of 84.0%, specificity of
90.0%) or 1.69 mg/l (sensitivity of 82.0%, specificity of 94.0%). A new constructed cys-C
based formula which requires kidney volume and body surface area for calculations is a
reliable marker of GFR comparingly with the neonatal referential clearance values.
Conclusions. Our results indicate CysC is more sensitive marker of GFR than Cr in the
newborns
