BUN (Berthelot) (B7551-120)
For in vitro diagnostic use in the quantitative colorimetric determination of urea nitrogen in serum.
The Berthelot reaction, in which ammonia reacts with hypochlorite, phenol, a catalyst, and alkali to produce a stable blue complex (indophenol) has been known for over 100 years but only relatively recently used in a method for serum urea. The use of sodium nitroferricyanide was introduced in 1962 and the substitution of salicylate for phenol was introduced in 1967. This procedure is based upon a modified Berthelot reaction wherein urease hydrolyzes urea to ammonia and carbamic acid. Carbamic acid spontaneously decomposes into ammonia and carbon dioxide. Ammonia reacts with salicylate, nitroferricyanide and an alkaline solution of hypochlorite to yield a blue-green chromophore which is measured photometrically and is proportional to the amount of urea in the sample.