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.