Enzymatic, colorimetric method (urease) modified Berthelot reaction.
Urea is the major end product of protein nitrogen metabolism. It is synthesized by the urea cycle in the liver from ammonia, which is produced by amino acid deamination. Urea is excreted mostly by the kidneys but minimal amounts are also excreted in sweat and degraded in the intestines by bacterial action.
The use of urease in BUN determinations was introduced by Marshall who measured the liberated ammonia by titration with an acid. Ammonia produced by urease action has also been measured by nesslerization and by the Berthelot reaction. Vitro Urea/BUN endpoint reagents use the modified Berthelot reaction.