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.

Evaluation of a radiometric method for determination of total and unsaturated iron-binding capacities and serum iron.

We describe an evaluation of the "RES-OMAT FE-59" radiometric kit (Mallinckrodt Australia Pty. Ltd.) for determination of total iron-binding capacity and unsaturated iron-binding capacity; serum iron may be calculated from total iron-binding capacity and unsaturated iron-binding capacity. Values obtained on patients' sera were compared with those obtained by continuous-flow analysis; correlation coefficients were 0.92, 0.93, and 0.88 for total iron-binding capacity, unsaturated iron-binding capacity, and iron, respectively. Precision between-run and within-run was almost identical and compares very favorably with that reported by Dixon [Ann. Clin. Biochem. 10, 127 (1973)] and that achieved in inter-laboratory surveys. Analytical recovery averaged only 83.5%, but results of analyses of sera with assigned or consensus values showed good accuracy. Satisfactory performance cannot be achieved with lyophilzed bovine quality-control materials. The kit has significant technical advantages over colorimetric methods and good short- and long-term analytical performance.