Comparison of three kits for the enzymatic determination of urea

A comparative evaluation of Beckman (A), Boehringer (B), and Calbiochem (C) kits for the enzymatic end-point determination of urea has been carried out. Acceptable within-day and day-to-day precision was obtained with all kits. The recoveries obtained fulfilled the criteria of Logan (CRC Critical Reviews in Clinical Laboratory Sciences, 1972, 3, 271-289). Correlation between the results obtained by all kit methods and the diacetyl monoxime continuous-flow method, the reference method in this study, was excellent, but all methods evidenced a net negative bias at urea levels up to at least 20 mmol/1. We recommend kit A as the most satisfactory for routine use, consider kit B to be in the main acceptable, and suggest that kit C has disadvantages regarding both the accuracy attainable with quality control materials and the lack of information on blank correction for interfering compounds.