Creatinine is a breakdown product of creatine phosphate and produced and excreted at a constant rate. Measurements are used to determine glomerular filtration rate (GFR) - a measure of kidney function. Creatinine clearance is frequently used as a means of standardizing exrection of other compounds as well. Measurements are routinely generated through the use of validated commercial kits and/or specific alternative methods (HESKA). These analyses can be validated and performed in either a GLP / cGMP and R&D method. There is an additional charge for GLP and cGMP methods as compared to R&D projects.