Caution: It is very important to know the method used to measure creatinine in a blood, serum, or plasma sample, as it will affect the formula for estimating GFR in children.
Read the following information BEFORE selecting a calculator.
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Currently, the best equation for estimating glomerular filtration rate (GFR) from serum creatinine in children is the Schwartz equation. Note that estimated GFR calculated using the original Schwartz equation will be influenced by the change to creatinine assays that are traceable to an isotope dilution mass spectroscopy (IDMS) reference measurement procedure. In general, IDMS-traceable creatinine methods will produce lower results, which, when used in the equation, will overestimate GFR. The overestimation may be as much as 20% to 40%. Thus, the estimated GFR may not accurately reflect the patient’s kidney function.
The original Schwartz equation GFR calculator was developed using the alkaline picrate (“Jaffe”) reaction with a protein-removal step and has been historically used with routine creatinine methods.
- The original Schwartz equation should be used for creatinine measured using a method that is NOT traceable to an IDMS reference-measurement procedure.
- For labs using an alkaline picrate (“Jaffe”) reaction, it is important to note that the lower serum total protein of infants and children may cause a greater error in creatinine relative to measurements in adults. At this time, it is recommended not to estimate GFR for children when using an alkaline picrate (“Jaffe”) method that has calibration traceable to IDMS. Further information is available.
The interim IDMS-traceable Schwartz equation GFR calculator is for use with enzymatic creatinine methods that have been recalibrated to be traceable to IDMS. At this time, it is recommended not to estimate GFR for children when using an alkaline picrate (“Jaffe”) method that has calibration traceable to IDMS. Further information is available.
Caution should be used when the sample is hemolyzed or has elevated bilirubin . These interferents generally cause a lower serum creatinine result, but the magnitude varies with specific enzymatic or alkaline picrate (“Jaffe”) methods.