The estimation of cholesterol in blood

Abstract

The methods which are in use at present for the colorimetric estimation of cholesterol in blood are either time-consuming or of questionable accuracy. In connection with a study of the blood lipoids in obesity, it seemed necessary to investigate further the question of a suitable cholesterol method. For some time now we have employed a procedure which is comparatively simple and we believe to be very satisfactory.

The method consists essentially in mixing one C.C. of whole blood, plasma or serum with 4-5 grams of plaster of Paris, drying, and extracting the powder directly with chloroform in a special extraction apparatus. The plaster of Paris is emptied into a small paper extraction shell (4 cm. long) and this inserted in a short test tube (2.5 × 6 cm.) in the bottom and sides of which are a number of small holes. This is now attached to a large cork on a small reflux condenser and the tube and cork inserted in the neck of a 150 C.C. extraction flask containing about 20-25 c.c. of chloroform. Extraction is continued for 30 minutes on an electric hot plate, the chloroform made up to some suitable volume, such as 20 c.c., filtered if necessary, and colorimetric estimation carried out with the aid of the Liebermann-Burchard reaction, according to the the technique of Grigaut and of Autenrieth and Funk. Brown colors do not develop as with the Bloor method. An aqueous solution of naphthol green B, which is permanent, is used as standard.

Since the cholesterol esters give the color reaction, as pointed out by Bloor, saponification is unnecessary. With this method perfect duplicates and quantitative recoveries of added cholesterol and cholesterol esters may be had.