Reference intervals for plasma apolipoprotein B determined with a standardized commercial immunoturbidimetric assay: results from the Framingham Offspring Study.

We evaluated a commercially available, standardized immunoturbidimetric assay for apolipoprotein (apo) B, the protein constituent of low-density lipoprotein (LDL), to establish reference ranges for men and women, and to determine the concentrations associated with increased risk of coronary heart disease (CHD). The between-run CV for assay of a normal-concentration control for this assay was 6.60%. The mean (+/-SD) apo B concentration was 1.03 +/- 0.24 g/L in 1880 men, significantly higher than the mean for 1944 women (0.96 +/- 0.26 g/L) participating in cycle 4 of the Framingham Offspring Study (P<0.001). An apo B value of 1.20 g/L corresponded roughly to the 75th percentile in men, similar to an LDL cholesterol concentration of 1.60 g/L, and subjects with concentrations greater than this were significantly more likely to have CHD than subjects with apo B concentrations less than 1.00 g/L, the approximate 50th percentile (P<0.05 in men and P<0.001 in women).