Comparison of three kits for the enzymatic determination of urea

SUMMARY 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 mrnol/I. 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. A large number of methods are available for the determination of plasma urea (Henry et al., 1974). Direct colorimetric methods and methods involving generation of ammonia by urease (EC 3.5.1.5) followed by colorimetry or other analytical technique