The DetectX^® Serum Creatinine Kit measures creatinine in serum and plasma samples. A creatinine standard, calibrated to a NIST creatinine standard, is provided to generate a standard curve. The color generating reaction is initiated with the Creatinine Detection Reagent. The assay utilizes a kinetic absorbance method to overcome interference by colored compounds in the sample. The concentration of creatinine is calculated using the delta of the optical density readings at 1 and 30 minutes. We offer a free Excel worksheet for concentration calculations.

Creatinine is a metabolite of phosphocreatine (p-creatine), a high-energy phosphate that can be utilized by tissues for the production of ATP. Creatine either comes from the diet or synthesized from the amino acids arginine, glycine, and methionine. Creatine and p-creatine are converted non-enzymatically to the metabolite creatinine, which diffuses into the blood and is excreted by the kidneys. In vivo, this conversion appears to be irreversible and in vitro it is favored by higher temperatures and lower pH. Measuring serum creatinine is one of the most commonly used indicators of renal function. A rise in blood creatinine levels is observed only with marked damage to functioning nephrons. A good indicator of kidney function is given by the creatinine clearance test. Creatinine clearance can be accurately calculated using serum creatinine concentration and taking into account the variables of sex, age, weight, and race.