The Use of Urograph for the Determination of Urea Nitrogen Concentration in Serum and Plasma.

The accuracy and precision of Urograph, a commercial preparation of chromatography papers designed for the determination of urea nitrogen in plasma and serum, were assessed. Results of duplicate determinations were compared with those of two acceptable quantitative procedures, (1) automated diacetyl monoxime and (2) modified Van Slyke and Cullen analysis. Values for serum specimens obtained by Urograph were significantly higher than those found by the Autoanalyzer method. The confidence limits for the Urograph procedure ranged from 12.5% for plasma to 26.6% for sera, whereas the corresponding values were 6.9% and 7.0% for Autoanalyzer. This lack of precision with Urograph appeared to be due mainly to the presence of a few strips in which only partial migration occurred. The papers yielded low values following 81/2 months of storage in the refrigerator; the test was temperature-sensitive.