Plasma lipoprotein(a) distribution in the Framingham Offspring Study as determined with a commercially available immunoturbidimetric assay.

The purpose of our research was to evaluate a commercially available, automated, immunoturbidimetric assay for lipoprotein(a) (Lp(a)), to determine the distribution of Lp(a) in the Framingham Offspring Study population, and to determine Lp(a) levels that may be useful for assessing coronary heart disease risk. The mean between-run coefficient of variation for this assay was 5.65%. Lp(a) concentration was slightly, but significantly, higher in 1949 white women (mean +/- S.D. 214 +/- 195 mg/l, median 150 mg/l) than in 1884 white men (mean +/- S.D. 200 +/- 193 mg/l, median 130 mg/l) participating in Cycle 4 of the Framingham Offspring Study (P = 0.0015). Lp(a) values of 300 mg/l and 500 mg/l corresponded to approximately the 75th and 90th percentiles, respectively, for both men and women, and subjects with concentrations greater than or equal to 500 mg/l were more likely to have coronary heart disease than subjects with an Lp(a) concentration less than 300 mg/l (P < 0.05 for men).

Reference intervals for plasma apolipoprotein A-1 determined with a standardized commercial immunoturbidimetric assay: results from the Framingham Offspring Study.

We have evaluated a commercially available, standardized immunoturbidimetric assay of apolipoprotein (apo) A-I, the major protein constituent of high-density lipoproteins (HDL). We determined the reference ranges of plasma apo A-I concentration for white men and women and related these values to the risk of coronary heart disease (CHD). The mean between-run CV for this assay was 2.9%. As determined with individuals participating cycle 4 of the Framingham Offspring Study, the mean (+/- SD) apo A-I concentration was 13% lower in 1879 men (1.34 +/- 0.23 g/L) than in 1939 women (1.54 +/- 0.28 g/L) (P<0.001). An apo A-I concentration of 1.20 g/L roughly corresponded to the 25th percentile value in men and the 5th percentile in women, and subjects with a concentration below this value were significantly more likely to have CHD than subjects wit a higher concentration (P<0.001).

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).

Modification of the dextran-Mg2+ high-density lipoprotein cholesterol precipitation method for use with previously frozen plasma.

Although dextran-Mg2+ precipitation produces accurate and precise results for high-density lipoprotein (HDL) cholesterol in fresh plasma and serum, precipitation of frozen specimens with triglycerides > 2.26 mmol/L (> 200 mg/dL) is difficult. We developed a modification that dilutes thawed samples by 35% and increases dextran-Mg2+ reagent to 15% of sample volume. Standard precipitations were performed on 62 fresh EDTA-treated plasma specimens; supernatant solutions were analyzed fresh and after freezing. Standard and modified methods were also performed on thawed, paired plasmas. In specimens with triglycerides < or = 2.26 mmol/L, HDL cholesterol results for all methods were similar. For triglycerides > 2.26 mmol/L, however, bias and precision were significantly affected by freezing, and 38.5% of samples with standard precipitation required additional procedures to produce clear supernatant solutions. HDL cholesterol concentrations for thawed samples with standard precipitation were significantly greater than for fresh samples (P < 0.02), but those for the modified method were not different from fresh samples, and only one specimen required additional steps to produce a clear supernate.