BACKGROUND
Creatine produced in the kidney, liver and pancreas is transported to the brain and muscle and phosphorylated. However, a small proportion of free creatine is converted irreversibly to creatinine in the muscular tissue in proportion to the muscle mass. The amount of creatinine excreted daily by an individual is relatively constant. Thus, urinary creatinine levels may be used to normalize the rate of excretion of other analtyes. Normal urinary creatinine values for men and women range from 9.7 – 24.7 and 7.9 – 14.2 mmol/24h respectively. Changes in excretion rate may be indicative of impaired renal metabolism.

PRINCIPLE
This is a colorimetric assay for the quantitative analysis of creatinine levels in urine. Urinary creatinine metabolite reacts with picric acid under alkaline conditions to produce an orange color which can be quantified by absorption spectroscopy near 500 nm wavelength. The difference in color intensity determined before and after addition of acid is a direct estimate of creatinine concentration.

APPLICATION
This inexpensive and reliable assay for the quantitative analysis of creatinine is primarily intended for normalizing analyte levels in human urine samples.