A single-reagent manual method for directly determining urea nitrogen in serum.

A direct method is described, in which a single reagent is used without deproteinization, for measuring blood urea nitrogen (BUN) in serum. The reagent is a mixture of diacetylmonoxime, antipyrine (phenazone), and arsenic pentoxide in acid solution. Lipemia, bilirubin to 25 mg/100 ml, hemoglobin to 1g/100 ml, and protein to 20g/100 ml do not affect the results. Beer’s law is followed at 460 nm for BUN concentrations as great as 100 mg/100 ml. The direct method compares favorably with a manual ureaseBerthelot color method and with the diacetylmonoxime procedure as automated for the Technicon SMA 6/60. The method (CV, 6.7%) can be completed in less than 20 mm. The reagent is stable for at least two months.