Micromethod for total serum cholesterol that eliminates interference by high bilirubin concentrations.

The analysis of pediatric serum for total cholesterol in the presence of high amounts of bilirubin presents special problems. The serum specimens are so small that a direct microor ultramicromethod has to be used, and consequently the error owing to bilirubin is impressive. In the proposed method, cholesterol is precipitated, along with other serum lipids, from only 20 .iliters of serum as a dextran sulfate-lipoprotein complex. The precipitate is dissolved in molar NaCI, treated with glacial acetic acid, and incubated for 5 mm at 70#{176}C. A ferric chloride-sulfuric acid reagent is then added and, after 20 mm at room temperature, the color is read at 560 nm. Total cholesterol values obtained by the proposed method are not statistically different from those obtained by the direct method of Pearson eta!. Bilirubin added to sera does not affect the results. Agreement was obtained with the stated cholesterol values for Versatol-A and Moni-trol II reference sera to which known amounts of cholesterol and bilirubin had been added by the manufactu rer.