Summary: The enzyme methodology employed in this reagent is based on the reaction first described by Talke and Schubert. To shorten and simplify the assay, the calculations are based on the discovery of Tiffany, et al. that urea concentration is proportional to absorbance change over a fixed time interval. The reaction is monitored by measuring the rate of decrease in absorbance at 340 nm as NADH is converted to NAD.