Urea is hydrolyzed by urease to ammonia and carbon dioxide. The ammonia is converted to glutamate by glutamate dehydrogenase (GlDH) in the presence of NADH and oxoglutarate.
The reaction is monitored kinetically at 340 nm by the rate of decrease in absórbanse resulting from the oxidation of NADH to NAD+, proportional to the concentration of urea present in the sample.