LOW-DENSITY-LIPOPROTEIN CHOLESTEROL CAN BE CHEMICALLY MEASURED - A NEW SUPERIOR METHOD

The association between elevated levels of low-density lipoprotein (LD L) cholesterol and an increased risk of premature coronary heart disea se (CHD) is well documented. Most clinical laboratories estimate LDL c holesterol concentrations according to the Friedewald formula. It prov ides a relatively reliable estimate of LDL cholesterol concentration, provided the triglyceride concentration is <200 mg/dL, However, the re liability is considerably decreased if the triglyceride concentration is greater than or equal to 400 mg/dl. The interactions between lipopr oteins and surfactants, divalent cations, sugars, and lectins were inv estigated, and we developed a new assay protocol to chemically measure the LDL cholesterol level in serum that does not require immunosepara tion or centrifugation, The assay protocol was evaluated by measuring serum samples obtained from 88 patients and 20 healthy volunteers, The triglyceride levels of the patient samples ranged from 66 to 2199 mg/ dL, and the samples were classified as <200 mg/dL (n = 36) and greater than or equal to 400 mg/dL (n = 52; 23, 3, and 26 patients had type I Ib, type III, and type IV hyperlipoproteinemia, respectively) for comp arative studies. The accuracy and precision of our assay protocol fulf illed the criteria of the NCEP Lipid Standardization Panel, and no mat rix effect influenced the measurements. The assay protocol is less sen sitive to LDL-I than to LDL-II and LDL-III. LDL cholesterol measuremen ts correlated well with those obtained by the ultracentrifugal assay o f normotriglyceridemic and hypertriglyceridemic samples. This evidence shows that the results obtained with our assay protocol are superior to those obtained with the Friedewald formula.