Studies of the accuracy of measurements of serum high density lipoprotein cholesterol levels.

Titration of serum lipoproteins with three different precipitants--heparin-MnCl2 92 mmol.L-1, dextran sulfate-MgSO4, and phosphotungstate-MgCl2--revealed gross errors in the high density lipoprotein cholesterol (HDL-C) levels measured in some hyperlipidemic sera. Dilution studies of eight normal sera with the phosphotungstate method revealed that the most reliable estimate of the HDL-C level was the level measured in the least diluted aliquot that yielded a good precipitate. With a heparin-MnCl2 kit, serial dilution of a lipemic serum demonstrated a requirement for a blank correction. Establishing an accurate estimate of the HDL-C level sometimes requires knowledge of the titration curve of the lipoprotein precipitant being used, a blank correction, and data obtained from dilution studies (or studies with increased precipitant levels) on the serum in question.