Determination of total urinary protein, combining Lowry sensitivity and biuret specificity

Gel filtration was used to remove non-protein-bound substances that interfere with measure-ment of urinary protein by an automated version of the biuret reaction. Nearly 98 % of the protein was accounted for, and accuracy and precision were acceptable. Interference from bile pigments or hemoglobin pigments can be eliminated, and specificity is increased. Additional Keyphrases AutoAnalyzer #{149} inter-ference removal Determination of total urinary protein is now more frequently requested of the clinical chemistry labora-tory, 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 in-efficient under clinical laboratory conditions. Concen-trations for total urinary protein vary widely, and nu-merous 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). Tur-bidimetric 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