Creatinine is commonly measured in urine and is a key benchmark for the normalization of a variety of urinary biomarkers. Serum creatinine levels, however, are a useful indicator of renal function and abnormal levels have been implicated in diabetes, cardiovascular, and circulatory diseases. Cayman’s Creatinine (serum) Colorimetric Assay is designed to measure creatinine levels in plasma and serum. The assay relies on the Jaffe' reaction, wherein a yellow/orange color forms when the metabolite is treated with alkaline picrate. The rate of color development is directly proportional to the concentration of creatinine in the sample and is measured at an absorbance between 490-500 nm. The kinetic nature of the assay eliminates interference from extraneous serum contaminants, such as lipids and bilirubin.