Measurements of serum cystatin C concentrations underestimate renal dysfunction in pediatric patients with chronic kidney disease.

BACKGROUND: In our clinical experience, cystatin C (CysC) concentrations are not as high as expected in patients with chronic kidney disease (CKD) and high-stage renal dysfunction. We therefore investigated whether measurements of serum CysC result in an underestimation of renal dysfunction in pediatric patients with CKD. METHODS: Glomerular filtration rate (GFR) was estimated from serum creatinine (Cr) concentration, using the equation Cr-GFR (%) = [0.30 × body length (m)/serum Cr] × 100; and from serum CysC concentration, using the equation Cys-GFR (%) = (0.70/serum CysC) × 100. We investigated the relationship between GFR estimated by these 2 equations. Patients aged 2-12 years were assorted into 5 groups, based on GFR-Cr categories of <12.5, ≥12.5 to <25, ≥25 to <50, ≥50 to <75, and ≥75%, and GFR-CysC/GFR-Cr ratios were compared in these 5 groups. RESULTS: The median GFR-CysC/GFR-Cr ratio in groups of patients with GFR-Cr of <12.5, ≥12.5 to <25, ≥25 to <50, ≥50 to <75, and ≥75% were 2.28, 1.48, 1.22, 1.18 and 0.98, respectively, with statistically significant differences between any two groups (p < 0.001). CONCLUSION: Measurements of serum CysC concentrations lead to underestimation of renal dysfunction in pediatric patients with CKD.

Reference serum cystatin C levels in Japanese children.

BACKGROUND: Single measurements of serum cystatin C (cysC) concentration have generally been used to determine glomerular filtration rate (GFR) in adults. Since GFR varies to some extent among children, we attempted to determine reference serum cysC concentrations for Japanese children. METHODS: Serum cysC concentrations were determined by a latex particle-enhanced turbidimetric immunoassay in children who did not present with kidney disease or infectious disease, and the relationship between age and serum cysC level was assessed. RESULTS: We found that reference serum cysC levels gradually decreased during the first year after birth, thereafter becoming constant. Mean serum cysC concentration in children aged 1 year (0.76 ± 0.10 mg/L) was slightly higher than in children aged ≥2 years (0.70 ± 0.09 mg/L). CONCLUSION: Our reference values will be applicable for screening renal function in Japanese children.