[Determination of the low protein concentration in biological fluids. Methodological aspects (the use of mathematical...

We investigated the effect of albumin/globulin ratio on the analytic error of protein determination. Several methods were used: Bradford, Lowry, pyrogallol-red, biuret, and sulfosalicylic acid. Reagents used in Lowry method exhibit higher affinity to globulins, whereas reagents used in other methods have higher affinity to albumins. Although the biuret method demonstrated equal efficiency in determining concentrations of various proteins low sensitivity of this method limits its clinical applicability. For other methods there was non-linear dependence of the analytic error on protein composition in the sample. Combination of two methods for protein determination (using one calibrator) completely removes the analytic error.