Diagnosis and Assessment of Disease
ÎHDL particles contain 1 - 5 molecules of apoA-I per particle, making apoA-I a general estimate of HDL particle number.
ÎTotal HDL-P, via nuclear magnetic resonance spectroscopy (NMR), includes all but prebeta HDL species and is a more accurate way to quantify HDL particle concentration.
Lipoprotein Particles Contain Variable Amounts of Cholesterol and Triglyceride1-3
ÎHistorically, plasma triglycerides (TG) have served as a surrogate measure of VLDL levels, while LDL-C and HDL-C values serve as indicators of the concentrations of LDL and HDL particles.
ÎLipoprotein particle cores vary in the amount (ratio) of cholesterol and TG present.
ÎBecause the amount of cholesterol carried inside lipoprotein particles is highly variable among individuals with the same measured cholesterol levels, even the most accurate cholesterol measurements will, for many individuals, provide an inaccurate measure of circulating lipoprotein particles.
Clinical Value of Alternate Measure of LDL Quantity3-7
ÎConcordance and discordance examine the variability of one laboratory measure at a defined value of the other.
• If, at a defined level of one biomarker there is a similar value of the other, the two measures are said to be concordant.
• Conversely, if one biomarker is substantially higher or lower at a defined level of the other biomarker, the values are judged to be discordant.
ÎAlthough highly correlated, alternate measures of LDL quantity are frequently discordant.
• LDL can be measured by the cholesterol carried in LDL particles (LDL-C) or by measures of LDL particle number (apoB and NMR LDL-P).
ÎIn the general population, discordance between cholesterol and particle number measures of LDL occurs in approximately half of all subjects.
• Among patients with metabolic syndrome or type 2 diabetes mellitus (DM) discordance is more frequent (40% of subjects with LDL-C < 70 mg/dL and 75% of subjects with LDL-C < 100 mg/dL have discordantly high LDL particle number).
ÎCardiovascular events track with measures of LDL particle number.1, 3, 5, 8
• When LDL particle number is elevated, coronary heart disease (CHD) events are increased. When LDL-P is low, CHD events are decreased.
• If LDL-C and LDL particle number are discordant, risk tracks with particle number not LDL-C.
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• When LDL-C is concordant with LDL particle number both measures are equally associated with CHD risk.
