Since plasma high-density lipoprotein (HDL) is known to be protective against coronary artery disease and plasma low-density lipoprotein (LDL) is atherogenic, measurement of the cholesterol (C) content of these lipoproteins is important for assessing cardiovascular risk, diagnosing lipid disorders, and monitoring lipid-modifying interventions. First a variety of heterogeneous assays (requiring manual pretreatment/separation step), then a variety of homogeneous assays (requiring no off-line pretreatment step) have recently become available for measuring HDL-C and LDL-C. We assessed the analytical performance of four homogeneous HDL-C and two homogeneous LDL-C methods in 120 human sera. For comparison, HDL-C and LDL-C were also determined by electrophoretic and heterogeneous methods. LDL-C was also estimated from two different formulas. Except for one of the homogeneous methods for HDL-C, the electrophoretic (OreferenceO) method for HDL-C and LDL-C generally correlated highly with the respective heterogeneous and homogeneous methods, and with the two LDL-C formulas. However, biases between the old and some of the new methods suggested unsatisfactory standardization. Given their simplicity and adaptability to automation, properly standardized new homogeneous methods may provide cost-effective alternatives to earlier manual and semi-automated methods measuring for HDL-C and LDL-C.Because analysis of serum lipid, lipoprotein, and apolipoprotein constituents is not always possible in freshly collected specimens, and published data often are conflicting or not available for newer methods, we examined the effect of various storage conditions (+4 degrees C, -10 degrees C, and -70 degrees C) on these analytes, often by measuring with a variety of methods. Statistically significant (p is less than 0.05) differences were common with both parametric and nonparametric statistics between the initial and subsequently measured lipid (total cholesterol and glycerol-blanked triglycerides), lipoprotein-cholesterol (HDL-C: two methods, LDL-C: four methods, and VLDL-C), and apolipoprotein A-I, B, and E concentrations. The differences, however, were generally small (rarely up to 10 percent) and inconsistent. Only the apoE concentration tended to decrease (up to 40 percent) under all storage conditions, and, out of all analytes, only the differences for storing apoE at -70 degrees C were significant with ANOVA analysis. Thus, in contrast to some earlier observations, most serum lipids, lipoprotein-cholesterol fractions, and apolipoproteins can be reliably measured by a variety of currently available methods in refrigerated or frozen specimens.In collaborative work, the clinical utility of various lipid, lipoprotein, and apolipoprotein measurements was assessed in patients with cardiovascular disease and postmenopausal women.
