GFR estimated from cystatin C versus creatinine in children born small for gestational age

BACKGROUND: Low birth weight caused by intrauterine growth restriction may be a risk factor for renal impairment in the adult life.

STUDY DESIGN: A cross-sectional study.

SETTING & PARTICIPANTS: 71 children aged 8 to 13 years living in the community of São Paulo, Brazil, were included in the study. Gestational age was within the normal range.

PREDICTORS: Birth weight (range, 2,052 to 3,560 g) divided into quartiles: 2,500 g or less; 2,501 to 2,740 g; 2,741 to 3,000 g; and greater than 3,000 g. Birth weight ascertained by birth records in 43 and by recall in 28 participants.

OUTCOMES & MEASUREMENTS: Cystatin C, creatinine, and glomerular filtration rate (GFR) estimated by equations using cystatin C (eGFR(cys)) or creatinine (eGFR(cr)).

RESULTS: Overall, mean serum creatinine level was 0.8 +/- 0.01 (SE) mg/dL (range, 0.7 to 1.1 mg/dL); mean plasma cystatin C level was 0.9 +/- 0.02 mg/L (range, 0.5 to 1.6 mg/L), and eGFR(cr) and eGFR(cys) were 102.4 +/- 2.16 (range, 66 to 140) and 91.8 +/- 2.46 mL/min/1.73 m(2) (range, 49 to 139 mL/min/1.73 m(2)), respectively. No differences were found for serum creatinine or eGFR(cr) values among the birth-weight quartiles. There was a significant linear trend of increasing cystatin C levels (decreasing eGFR(cys)) in the lower birth-weight quartile groups (P = 0.002 and P = 0.02, respectively). Systolic blood pressure correlated with plasma cystatin C level (r = 0.31; P = 0.008) and eGFR(cys) (r = -0.26; P = 0.028). Covariance analysis adjusting for age, sex, body mass index for age compared with standards of the National Center for Health Statistics and expressed as a z score, and systolic blood pressure showed that cystatin C values remained greater in the lowest than highest birth-weight quartile (1.01 +/- 0.05 versus 0.83 +/- 0.05 mg/L; P = 0.02).

LIMITATIONS: Ascertainment of birth weight by recall in some participants. Lack of measurement of microalbuminuria, absence of direct GFR measurement, and small sample size.

CONCLUSIONS: Lower birth weight is associated with higher levels of cystatin C but not creatinine in 8-13 yr. old children born full-term.