BUN Interference Comparison Urea is one of the few serum analytes which can be measured using ultraviolet detection without serious chromatic interference. The reason can be seen from the molar concentration at the upper limit of normal. Urea is one of the most plentiful molecules in serum. Additionally, two molecules of NADH are oxidized per molecule of urea. Thus, the signal [chromophore absorbance] to noise [serum background absorbance] is very favorable, relative to other serum analytes.
The Synermed® blood urea (BUN) method is based on the enzymatic conversion of urea to two molecules of ammonia. The ammonia participates in an enzymatic reaction with glutamate dehydrogenase in which NADH is oxidized to NAD. The rate of decrease in absorbance of NADH at 340 nm is proportional to urea concentration.
The reagents are supplied as stable ready-to-use liquids for simplicity of use. The extended "on board" life of the reagents results in economies due to the elimination of wastage and reconstitution time.
urea + H20 -> 2 NH3 + CO2
2 α-ketoglutarate + 2 NH4+ + 2 NADH -> 2 L-glutamate + 2 NAD+ + 2 H20