New Refractometric Methods for the Determination of Total Proteins in Serum and in Urine

New, precise, physical methods for the determination of total protein in serum or plasma and in urine are described. They are based upon the refractometric determi-nation of total solids in these fluids before and after protein has been removed by coagulation and, in ordinary use, they require no special standardization or calibra-tion. The urine method is applicable primarily to protein concentrations above 100 mg./100 ml. A by-product of the urine method is the direct and simple determination of the nonprotein specific gravity of proteinuric urine. I.. EFIiACTOMETIUC ME’rnol)s have been successfully applied to the pre-cise determination of the total solids of serum and urine, of the specific gravity of these fluids, and of related variables (1-3). Total proteins of serum niay also be estimated refractometrically (4-7) but with low-er accuracy (ca. ± 0.15 to ± 0.4 gm./100 ml.), depending in part upon the degree of lipemia and the variability of the other nonprotein solids. We report here new methods for the measurement of protein ill se-rum and in urine based upon the ref ractometric determination of total solids in these fluids before and after protein has been removed by coagulation. In ordinary use, no special standardization or calibration is necessary. hi addition, a new and simple method is presented to ob-tam the nonprotein specific gravity of urine containing protein. Briefly, the methods consist of the following. An 0.2-mi. sample of serum is drawn into an acetic acid-treated syringe. The refractive in