Predictive value of amniotic fluid cystatin C levels for the early identification of fetuses with obstructive uropathies

Objective: To compare the diagnostic accuracy of cystatin C with that of creatinine in discriminating renal function in fetuses without ultrasononographic evidence of renal malformations from those with obstructive uropathies. Design: Prospective, observational cohort study. Setting: Prenatal morphologic and functional evaluation of fetal obstructive uropathies throughout pregnancy. Population: A total of 96 healthy pregnant women at different stages of pregnancy, without any pregnancy-related maternal disease. Eighty-one pregnant women without clinical and ultrasonographic evidence of any fetal anomaly, confirmed at birth, were defined as controls; 15 pregnant women with various fetal obstructive uropathies, evidenced by repeated ultrasound examinations and confirmed at birth, were defined as cases. Methods: Creatinine was measured by a kinetic Jaffe picric acid method and cystatin C by a nephelometric immunoassay. Variables were analysed by applying conventional statistical tests; the non-parametric receiver operating curves (ROC) analysis was used to evaluate the diagnostic efficiencies of the biochemical markers. Main outcome measures: Incidence of confirmed, diagnosed, neonatal obstructive uropathy by measuring baseline levels of cystatin C and creatinine in amniotic fluid. Results: Baseline levels of cystatin C in amniotic fluid were significantly higher (P = 0.0015) among cases than in controls with comparable gestational age; no significant difference was found for creatinine levels (P = n.s.). The maximum diagnostic accuracy of serum cystatin C in discriminating controls from fetal uropathies was 96%, while that of creatinine was 62%. Conclusion: Cystatin C may be considered a sensitive biochemical marker for the early identification of fetuses with obstructive uropathies.