Plasma lipoprotein analysis: relative precision of total cholesterol and lipoprotein-cholesterol measurements in 12 lipid-research-clinics laboratories.

The 12 laboratories of the North American Lipid Research Clinics performed lipid and lipoprotein analyses on aliquots of 53 freshly prepared plasma samples during four years. The samples, from normal, mildly hyperlipidemic, and treated hyperlipidemic subjects, were analyzed for total cholesterol, triglycerides, and cholesterol in verylow-density lipoproteins (VLDL), low-density lipoproteins (LDL), and high-density lipoproteins (HDL). The data were used to estimate the overall variability of lipoproteincholesterol measurements as compared with that of total cholesterol measurements in the 12 laboratories. The overall CVs for total cholesterol measurements were 2.5 and 2.1 % for analyses performed with the AutoAnalyzer-l and -Il, respectively. The corresponding CVs for triglyceride analyses were 5.0 and 5.7%. The results agreed well with those reported previously. Variabilities in VLDL-, LDL-, and HDL-cholesterol measurements were 2.5-3.5 times those for total cholesterol. Much of this increase was accounted for by the random component of variability and was probably caused by manipulations necessary to prepare the lipoprotein fractions for analysis. A qualitative assessment of the presence or absence of f3-VLDL (“floating beta” lipoproteins), “sinking prebeta” lipoproteins, chylomicrons, and plasma turbidity, was made in 27 samples. The number of samples for which unanimity of interpretation was attained was used as a measure of comparability. The proportion of samples for which complete agreement was reached for the four components was: chylomicrons, 78%; f3-VLDL, 74%; “sinking prebeta” lipoproteins, 56%; plasma turbidity, 37%. The proportion of samples for which at least three quarters of the laboratories agreed was: chylomicrons, 89%: fl-VLDL, 93%; “sinking prebeta” lipoproteins, 70%; plasma turbidity, 85%.