Fetal serum concentrations of cystatin C and beta(2)-microglobulin as predictors of postnatal kidney function

OBJECTIVES: Cystatin C and beta (2)-Microglobulin are established serum mar kers of renal function in children and adults. In contrast to creatinine, d iaplacental exchange is minimal. The aim of the study was to establish refe rence values in fetal serum and to test their efficiency in predicting post natal kidney function. STUDY DESIGN: This was a prospective noninterventional study measuring cyst atin C and beta (2)-microglobulin by particle-enhanced immunoturbidimetry i n excess serum from 129 cordocenteses performed in 84 fetuses. Reference in tervals (mean +/- 1.96 SD) were calculated in a subgroup of 54 fetuses with out evidence of kidney disease, and these reference values were evaluated i n 75 sera from 55 fetuses. RESULTS: Mean cystatin C was 1.66 +/- 0.202 mg/L (upper limit 2.06), and me an beta (2)-microglobulin was 4.25 +/- 0.734 mg/L. Unlike cystatin C, beta (2)-microglobulin decreased significantly with gestational age so that the upper reference limit was 7.19-0.052 x gestational age in weeks. beta (2)-M icroglobulin had higher sensitivity (90.0% vs 63.6%) and cystatin C a highe r specificity (91.8% vs 85.5%) for the prediction of impaired renal functio n; diagnostic efficiency was equal (87.6% vs 86.1%). Fetuses with impaired renal function at birth or who were aborted for renal malformations had hig her cystatin C concentrations than those in a control group. beta (2)-Micro globulin was increased only in fetuses who were aborted. CONCLUSION: Fetal serum cystatin C and beta (2)-microglobulin concentration s may be useful predictors of postnatal kidney function.