An improved method for the rapid assessment of persisting chylomicron remnant concentrations.

Persisting chylomicron remnant concentrations have been linked to premature atherosclerosis. The analysis of persisting chylomicron remnant concentrations by an oral triglyceride tolerance test, however, is time-consuming for the study subjects and requires large resources in the laboratory. Therefore, only small numbers of subjects have been studied in the past. We describe major improvements of the testing procedure in regard of composition of the fatty meal, of patient testing, and measurement of postprandial remnants. Shifting the time of the (ready-to-use) fatty drink from the morning hours to bedtime was well accepted by the study subjects and allowed the analysis of blood samples drawn at the morning with minimal impact on the participants' time and with minimal interferences by confounding factors (e.g. smoking, additional food intake, physical activity). Chylomicron remnants were measured by fluorometry of the supernatant after ultracentrifugation. This procedure was sensitive, was specific for chylomicron remnants, and was easy to perform. The biological validity of the improved procedure was evaluated by studying type III hyperlipoproteinemia patients and normolipemic apolipoprotein (Apo) E2 homozygotes. In conclusion, this improved test permits the rapid testing for persisting chylomicron remnants in the clinical routine and in large epidemiological studies.

Comparison of an immunoprecipitation method for direct measurement of LDL-cholesterol with beta-quantification (ultracentrifugation).

A direct LDL cholesterol assay was evaluated using immunoprecipitation (Sigma Diagnostics, St. Louis, MO) with beta-quantification obtained by ultracentrifugation. Excellent intra- and interassay coefficients of variation were obtained (< 4.5%). There was a good correlation (r = 0.88, P < .0001) between the two methods for low-density lipoprotein cholesterol (LDL-C) in 249 samples with triglyceride levels ranging from 13 mg/dL to 2,236 mg/dL and LDL cholesterol levels ranging from 28 mg/dL to 290 mg/dL. Similar correlations were seen for patients with triglyceride levels < 400 mg/dL (r = 0.89, n = 174) and > or = 400 mg/dL (r = 0.89, n = 75). However, using the Friedewald equation, there was a good correlation only in samples with triglyceride levels < 400 mg/dL. No significant differences were found between LDL-C quantitated by the direct LDL assay and beta quantification for patients with dysbetalipoproteinemia (Type III disorder). However, calculated LDL values using the Friedewald equation were found to be significantly higher when compared to beta-quantification in patients with the Type III disorder. There was a slight but significant decrease in LDL-C determined by direct LDL cholesterol assay for non-fasting versus fasting serum (4.7%) despite a strong correlation between these samples (r = 0.98, P < .0001). In addition, freezing samples for 30 days resulted in a significant decrease in levels (15.1%). Thus, this direct LDL cholesterol assay is recommended in place of beta-quantification in hypertriglyceridemic samples (TG > or = 400 mg/dL) and to monitor LDL cholesterol levels in patients with Type III dyslipidemia, because it is less time consuming, more cost-effective and can be adapted to the clinical laboratory.