Manual and automated methods for urea nitrogen measurement in whole serum.

A simple method is described for directly determining serum urea nitrogen, wtihout deproteinization. The urea in 20 Ml of serum or plasma is reacted with diacetylmonoxime in the presence of thiosemicarbazide and cadmium ion under acid conditions. The absorbance of the resulting rose-purple solution is measured at 540 nm. Results agreed excellently with those obtained by a reference method that makes use of urease and the Berthelot phenate-hypochlorite reaction for ammonia. An automated adaptation utilizing the AutoAnalyzer is also described, which eliminates the need for a dialyzer. A further advantage is that the same reagents are used for both methods.