Determination of total urinary protein by combined gel filtration and automated biuret reaction.

Determination of total urinary protein is now more frequently requested of the clinical chemistry laboratory, one reason being the increased number of patients with renal transplants for whom total urinary protein is determined as an index of immunological rejection (1). Available manual methods are cumbersome and inefficient under clinical laboratory conditions. Concentrations for total urinary protein vary widely, and numerous interfering substances prevent direct analysis by the biuret reaction (2, 3). It has been necessary first to isolate and purify the protein, usually by precipitation (4), and to determine a blank correction (5). Turbidimetric methods have also been used (6). Current methods do not adequately remove interferences caused by biliuria and hemoglobinuria. Most nonspecific substances that interfere with the biuret reaction are non-protein-bound compounds of low molecular weight. Others are bound more or less strongly to the protein. Gel filtration eliminates most of the interference by isolating the protein. The ab-