Measurement of total protein and albumin in serum with a centrifugal analyzer.

In most clinical chemistry laboratories, mechanized procedures are essential for measurement of serum total protein and albumin. The biuret reaction is well established as the most practical approach to mechanized total protein measurements (1-4); albumin has posed a more difficult problem, with several procedures being proposed, some of which have involved salt fractionation (1-4), electrophoresis (5), dye binding (6-9), or total globulin measurements (10, 11). Dye binding offers the most convenient procedure for automation, but suffers inherent inaccuracies. 2-(4’-Hydroxybenzeneazo)-benzoic acid has been used extensively (6, 7) butis quite inaccurate (11). The bromcresol green (BCG) procedure is more accurate (8, 9), although a recent report questions the specificity of the reaction (12). However, it is easily adapted to automation and at the present time appears to be the reagent of choice. Automated continuous-flow systems are widely used to measure total protein and albumin. Another approach to automation, however, is the centrifugal analyzer, which offers a great deal of flexibility to the clinical laboratory. These instruments are ideally suited to kinetic measurements but can also be applied to conventional end-point determinations. A kinetic total protein procedure has been reported (13) for use with the centrifugal analyzer, but in our hands the method was found to be relatively imprecise and subject to errors in analyses of sera from patients with dysproteinemias. More conventional approaches to adaptation of the biuret reaction for use with the centrifugal analyzer have also been reported (14, 15). Here, we evaluate procedures adapted to the centrifugal analyzer for serum total protein and albumin, by the biuret reagent and BCG, respectively.