[Beta 2 microglobulin in the serum as a parameter of glomerular kidney function in the first days of life].

Though serum creatinine is a very reliable parameter for predicting glomerular filtration rate in infancy, this does not apply to the first hours and days of life. As there is no placental barrier for creatinine, serum creatinine at birth reflects maternal renal function at the moment of delivery and, during the first days of life, establishment of the steady state condition between creatinine serum level and actual infantile glomerular filtration rate. Serum creatinine levels of cord blood and maternal blood in term and preterm infants of 25-42 weeks gestational age are almost identical (maternal blood 0.82 +/- 0.34 mg-%, cord blood 0.87 +/- 0.34 mg-%, n = 77, r = 0.94), whereas there is no correlation between maternal and infantile beta 2-microglobulin concentrations (maternal blood 2.1 + 1 mg/1, cord blood 3.3 +/- 0.6 mg/l, n = 78, r = 0.05). There is no free diaplacental exchange for this low molecular weight protein. The determination of cord blood beta 2-microglobulin levels therefore predicts the newborn's renal function independently of the mother's. It is possible to differentiate between prenatal and perinatal genesis of renal damage in case of renal failure in the newborn, and to study the elimination of creatinine preloading in maternal renal insufficiency. Although we are not yet able to give an exact quantitative prediction of glomerular filtration rate by determining beta 2-microglobulin we believe it to be the best parameter of glomerular renal function in this age-group.