How to establish glomerular filtration rate in children

The availability of a world-wide standard for creatinine is an important milestone improving glomerular filtration rate (GFR) estimations in adults. However, an unacceptable inter-laboratory variation is still observed which is mainly due to differences in calibration, especially in children and infants, where reference ranges for serum and plasma creatinine are low. Compensating calibration in Jaffe assays to IDMS standards results in an underestimation of serum or plasma creatinine due to the lower reference values for total protein in younger children. Alternatively, using enzymatic assays emphasizes the relative proportion of tubular secretion of creatinine, which renders serum or plasma creatinine less suited as a GFR marker in children. Updating the currently used estimation formulas for calculating creatinine clearance and GFR is far from easy. Low molecular mass marker proteins such as cystatin C and beta trace protein can be regarded as an attractive practical alternative for assessing GFR since they require determination only in serum or plasma and are better suited in the blind range of creatinine.