Determination of Serum Proteins.

Abstract

There have been two methods for the estimation of the serum proteins, the refractometric and the chemical determination of the nitrogen through some modification of the Kjeldahl method. While titrating proteins electrometrically we found that the amount of acid required within certain ranges to take a protein from one pH to another was a direct function of the concentration of the protein actually present. This offered an ideal and simple method for the estimation of the serum proteins in the normal and pathological blood. For clinical purposes this can be done with indicators of which we have found methyl red the most satisfactory, and for more exact estimations, the hydrogen ion concentration can be determined electrometrically.

For the colorimetric estimation of the proteins in the serum the following method is used. One-half cc. of blood is diluted with an equal quantity of distilled water and one-quarter cc. of tenth normal HCl and 2 drops of methyl red are added. A color develops instantly.

Yellow—over 6% Protein.

Yellow orange—5% Protein.

Pink orange—4% Protein.

Pink—3% Protein.

Red—below 3% Protein.

This furnishes results sufficiently accurate for ordinary clinical purposes. If more accurate results are required a set of acetate buffers are made up between the ranges of pH = 4 and pH = 6. The serum proteins may then be matched as follows:

7.2%—–pH 6.2 4.5%—–pH 5.3

6.3%—–pH 5.9 3.6%—–pH 5.0

5.4%—–pH 5.6 2.7%—–pH 4.7

The application of protein titration given above is entirely designed for clinical purposes. The results when compared with buffer solutions give results that check within 0.4-0.5 gm. of protein per 100 cc. of serum with those obtained by the determination of the total protein nitrogen by digestion methods. This is sufficiently accurate for diagnostic purposes. One hundred sera were examined and parallel determinations of the serum protein nitrogen made and were found to be within this limit.