Clinical Chemistry, Vol 16, 18-19, Copyright © 1970 by the American Association for Clinical Chemistry

Micromethod for Total Serum Cholesterol that Eliminates Interference by High Bilirubin Concentrations

¹ Division of Biochemistry, Walter Reed Army Institute of Research, Walter Reed Army Medical Center, Washington, D. C. 20012.

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 micro- or 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 µliters of serum as a dextran sulfate—lipoprotein complex. The precipitate is dissolved in molar NaCl, treated with glacial acetic acid, and incubated for 5 min at 70°C. A ferric chloride—sulfuric acid reagent is then added and, after 20 min 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 et al. 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 manufacturer.