|The Creatinine Companion is a chemical assay designed to monitor urinary creatinine in a convenient microplate format. It is intended as a "companion" for Exocell urinary albumin assays.
The assay is based upon the Jaffe' reaction of alkaline picrate with creatinine. Standards or samples are added to a microplate, and alkaline picrate reagent is added. Absorbance at 500 nm is determined after a 10 minute incubation on the benchtop. Subsequently, an acid solution is added, and absorbance is again determined after a 5 minute incubation. The difference between these absorbance values is directly proportional to the the creatinine concentration, and a standard curve is generated from the response to the standards. Unknown samples are evaluated by comparing response to the standard curve. The assay may be completed in less than 30 minutes.
The assay serves as a normalization procedure for other analytes in urine samples, particularly for urinary albumin (1,2). It allows for a measure of kidney function based on a spot urine sample rather than the usual 24 hour pool.