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The dual-precipitation method for measurement of cholesterol in high-density lipoprotein subfractions HDL2 and HDL3 (Warnick et al., Clin Chem 1982;28:1574) was compared with quantification of cholesterol in HDL2 and HDL3 by zonal ultracentrifugation (Patsch et al., J Lipid Res 1974;15:356-66). For 39 plasma specimens differing widely in their HDL subfraction cholesterol concentration, the coefficient of correlation between the two methods was 0.94 for HDL2-cholesterol, 0.82 for HDL3-cholesterol. Storage of plasma specimens at -70 degrees C decreased the apparent content of HDL3-cholesterol by 5%; no significant changes in HDL2-cholesterol were observed. In frozen plasma, interference by apoB-containing lipoproteins and by lipoprotein(a) was negligible. Mean weight ratios of apoA-I to cholesterol were twice as high for HDL3 as for HDL2, reflecting the increased cholesterol content of HDL2. The study suggests that quantification of HDL2 and HDL3 cholesterol by precipitation is appropriate for use in epidemiological studies.
Patsch et al. (Wed,) studied this question.