Estimating Equations for Glomerular Filtration Rate in Children: Laboratory Considerations

Abstract

A recent report by Schwartz and coworkers has described improved equations for estimating glomerular filtration rate (GFR)1 in children (1). The equations were developed with data collected from 349 children 1–16 years of age with GFRs of approximately 20–90 mL · min−1 · (1.73 m2)−1 who were enrolled in the Chronic Kidney Disease in Children (CKiD) study. The new equations were developed to meet the specific need for estimating GFR in this study group, but they have broader applicability for clinical practice. Estimated GFR (eGFR) is useful to classify chronic kidney disease and to make adjustments in drug dosage. Changes in creatinine measurement procedures and calibration since the 1970s, when the original Schwartz equation to estimate GFR in children was published, have caused this equation to overestimate GFR compared with the measured GFR. The report by Schwartz and coworkers (1) presents a revision of the original Schwartz equation. Like the original equation, the revised equation is based on height and creatinine measurements, but the new equation uses creatinine as measured by an enzymatic method with calibration traceable to an isotope dilution mass spectrometry (IDMS) reference measurement procedure. This updated Schwartz equation should be suitable for use with clinical laboratory methods for measuring creatinine that have similar performance and calibration traceability. The updated equation now appears on the National …