Kidney function reference values in US adolescents: National health and nutrition examination survey 1999-2008

Background and objectives Few data are available on kidney function in normal US adolescents. This study characterizes the distribution of kidney function measures and associated factors. Design, setting, participants, & measurements Serum creatinine, cystatin C, and urinary albumin-to-creatinine ratios were measured in US adolescents (aged 12 to 17 years; n = 5575) in the cross-sectional National Health and Nutrition Examination Survey 1999-2008. The reference population was defined as healthy adolescents with BP <120/80 mmHg and a Z-score for weight-to-height ≤1.645, without self-reported diabetes or hypertension, not using prescription medications in the preceding 30 days, not pregnant or currently menstruating. Results were analyzed by age, gender, race, ethnicity, body mass index, and BP; estimated GFR (eGFR) was calculated using the original and revised Schwartz formulas. Results Mean values for eGFR _{Schwartz original formula}, serum creatinine, and serum cystatin C were 147 ml/ min/1.73 m ², 0.71 mg/dl, 0.82 mg/L, respectively. The median urinary albumin-to-creatinine ratio was 6.8 mg/g creatinine. In the reference population (n = 2881), eGFR differed significantly using the two Schwartz formulas; values were higher using the original formula (median values 143 versus 96 ml/min/1.73 m ²). Serum creatinine level (0.7 versus 0.72 mg/dl), but not cystatin C level (0.82 versus 0.82 mg/L), was lower in the reference population than in a nonreference population of adolescents. Conclusions These findings provide important demographic information and highlight the need for confirmatory testing of the revised Schwartz formula by comparison to measured GFR in healthy US adolescents.