Cholesterol methodology for human studies

A classification and review of the methodology involved in the determination of serum cholesterol for human (or animal) studies are presented. The purpose of both is to enable selection of a technique appropriate for the assay intended with a reasonable understanding of its advantages, disadvantages and limitations. The various methods discussed include direct reaction systems, partial isolation systems and complete isolation systems, as well as screening, reference and definitive procedures. The interferences that could occur are considered, especially those caused by hemoglobin, the turbidity in lipidemia, and bilirubin, as well as interferences caused by optical aberrations and chemical reactants. The various instrumental methods used to determine cholesterol or a substitute determinand such as hydrogem peroxide are discussed, including spectrophotometry, electrochemistry and densitometry of electrophoretically separated proteins.

Comparative determination of plasma phospholipids by automated gas--liquid chromatographic and manual colorimetric phosphorus methods

Plasma samples obtained during a prevalence study of hyperlipemia in a free-living urban population were analyzed for phosphatidylcholine, sphingomyelin and lysophosphatidylcholine content by automated high-temperature gas--liquid chromatographic (GLC) and manual colorimetric phosphorus (thin-layer chromatographic, TLC) methods. The GLC estimates were obtained from a quantitative analysis of the diacylglycerol, ceramide and monoacylglycerol moieties released from the parent phospholipids by digestion with phospholipase C, while the TLC estimates were derived by manual colorimetric phosphorus analyses of the individual phospholipid classes resolved by TLC. On samples analyzed over a two-year period the methods gave excellent correlation for the total phospholipids (r = 0.98), phosphatidylcholine (r = 0.98) and sphingomyelin (r = 0.90), but resulted in a poor agreement for lysophosphatidylcholine (r = 0.69). Comparable results were obtained for estimates of these phospholipids in plasma very low density, low density and high density lipoproteins. The between-method coefficient of variation ranged from 3 to 5% for phosphatidylcholine and from 5 to 10% for sphingomyelin. The relative error for the estimates of lysophosphatidylcholine ranged from 10 to 25%, and was due to the inclusion in the GLC estimates of a variable proportion of plasma free monoacylglycerols. Other differences between the two methods are due to various analytical errors and biases inherent in the two techniques. The within-day, within GLC, relative error averaged 1% for phosphatidylcholine, 3% for sphingomyelin and 5% for lysophosphatidylcholine. The apparent high precision and accuracy of the GLC method recommend it as an alternative to conventional direct methods of phospholipid analyses based on TLC isolation of lipid classes and colorimetric measurements of their phosphorus content. The GLC analyses of the plasma phospholipids are particularly convenient in conjunction with GLC measurements of plasma cholesterol and triacylglycerols, where a smaller throughput of samples is not a limitation and where both total amount and relative proportion of the lipids are of interest.

Determination of free, total, and esterified cholesterol by high-performance liquid chromatography

A method is described for measuring free, total, and esterified cholesterol in blood serum in which reversed-phase liquid chromatography is used and the eluate is monitored at 200 nm. The sample for total cholesterol is prepared according to the Abell-Kendall procedure, and for free cholesterol an extract of serum--isopropanol (1:5, v/v) is used. The column is a muBondapak C18, 10 micrometers, and the mobile phase for total cholesterol is isopropanol--acetonitrile (50:50, v/v); for free cholesterol, it is isopropanol--acetonitrile--water (60:30:10). An approximation of the free cholesterol, triglycerides, and individual cholesteryl esters is obtained from single chromatograms of isopropanol extracts of serum if the first mobile phase is used. In a comparison study with the Abell-Kendall method for total cholesterol, the correlation is excellent and the precision is acceptable.

Comparative determination of plasma cholesterol and triacylglycerol levels by automated gas--liquid chromatographic and autoanalyzer methods

Plasma samples obtained during a prevalence study of hyperlipemia in a free living urban population were analyzed for total cholesterol and triacylglycerol content by automated high-temperature gas--liquid chromatographic (GLC) and automated colorimetric (Auto-Analyzer, AA11) methods. The analyses were done over a three-year period. The methods gave excellent overall correlation for both total cholesterol (r = 0.9811) and total triacylglycerols (r = 0.9739). Detailed comparisons of the results obtained by the two methods with natural samples over the entire concentration range, indicated that the GLC method gave cholesterol values 5--10 mg% lower and triacylglycerol values 10--20 mg% lower than the corresponding AA11 determinations. The differences between the two methods are attributed to an overestimation of the cholesterol and triacylglycerol levels by the AA11 method due to presence of variable amounts of interfering chromogens in the plasma extracts. The between-method relative error ranged from 3 to 5% for cholesterol and from 5 to 10% for triacylglycerols. The within-day standard deviation of GLC averaged 2.3 mg% for cholesterol and 3.5 mg% for triacylglycerols. The between-day standard deviation of the GLC method averaged about 6 mg% for both cholesterol and triacylglycerols. The within-day, within GLC, relative error averaged 1.12% for cholesterol and 2.66% for triacylglycerols. The apparent high precision and high accuracy of the GLC method recommend it as an alternative to the indirect methods of plasma cholesterol and triacylglycerol analysis, especially where a smaller throughput of samples is not a limitation and where both total amount and composition of the lipids is of interest.