Isotope Dilution Mass Spectrometry (IDMS): In an effort to reduce interlaboratory variation in creatinine assay calibration and allow for more accurate estimates of glomerular filtration rate (GFR), the Creatinine Standardization Program was created.

This effort is a result of a collaboration among the National Kidney Disease Education Program’s Laboratory Working Group, the International Federation of Clinical Chemistry and Laboratory Medicine, and the European Communities Confederation of Clinical Chemistry. The NKDEP states that this, "The effort is part of a larger NKDEP initiative to help providers better identify and treat chronic kidney disease in order to prevent or delay kidney failure and improve patient outcomes." If you are not sure, please call your institution’s lab or contacted laboratory to determine if they meet these new standards. If using the pediatric GFR calculator it is also important to note that it is not recommended to estimate GFR for children when using an alkaline picrate (“Jaffe”) method that has calibration traceable to IDMS. Furthermore, it is important to use caution when the blood sample is hemolyzed or has evidence of elevated bilirubin as they can interfere with the lab assays thereby causing a lower serum creatinine result. The magnitude of variation also differs with specific enzymatic or alkaline picrate ("Jaffe") methods.