Comparison of LDL Particle Count With Other Available Lipid Tests

Overview

Despite the wide availability of advanced lipoprotein tests, no reference standard exists for Low Density Lipoprotein Cholesterol (LDL-C) due to inherent problems with each of the assays. Newer methods for estimating LDL particle numbers, including nuclear magnetic resonance (NMR) spectroscopy and vertical auto profile (VAP) are currently under investigation. NMR has been proposed as having the best correlation with adverse cardiovascular outcomes. Unfortunately, the accuracy of LDL-C or LDL particle number measurements is currently not monitored by national standardization programs. Direct comparisons between the various testing methods have been limited restricting our ability to accurately interpret and compare values across vendors and lipid parameters. Our hypothesis is that: 1. LDL particle count numbers, as determined by NMR (Liposcience), provides the best estimates of cardiovascular risk. 2. Discrepancies exist between the LDL particle count by NMR and other values as presented by calculated LDLC and directly measured LDL (VAP and ion mobility). The investigators will enroll 100 patients recruited from the Lipid Clinic at the Scripps Center for Integrative Medicine. Each patient will have one blood draw from which four tests will be analyzed. Risks are associated with drawing blood, which will be minimized by using Scripps Clinic Lab technicians. The potential loss of personal health information will be reduced by limiting access to study and lab staff and keeping information password-protected on Scripps servers.

Introduction Advanced lipoprotein testing has been available for over 50 years and its use in cardiovascular risk stratification has been proposed in a number of clinical trials (Superko 2009, 2383). Low Density Lipid Cholesterol (LDLC) is currently used as the key cardiovascular biomarker for assessing risk and monitoring response to lipid therapy (Cole, T. 2013, 752). The highest correlation with cardiovascular risk has been found with apolipoproteinB (apoB) or LDL particle concentration by NMR (Brunzell 2008, 814). Despite the wide availability of advanced lipoprotein tests, no reference standard exists for LDLC due to inherent problems with each of the assays (Mora 2009, 2402)(Marcovina 2006, 440). The most common laboratory method of determining LDLC is by precipitation of apolipoproteinB (apoB) containing lipoprotein particles, measurement of the high density lipoprotein cholesterol (HDLC), and calculation of the LDLC by the Friedewald equation; however, there are inherent errors associated with three separate measurements (Marcovina 2006, Superko 2009, 2384). Correlation between lab LDLC and values obtained by ultracentrifugation has been reported to range from 7 to 31.2%, with a significant amount of misclassification (Marcovina, S. and Packard, C. 2006, 440). Furthermore, elevated triglycerides have been reported to interfere with the accuracy of LDLC measurements (Marcovina, S. and Packard, C. 2006, 440). ApoB, which is the main protein component of LDL, is also considered a direct measure of LDL particle number (Cole, T. 2013, 753). Newer methods for estimating LDL particle number, including NMR and VAP are currently under investigation. NMR has been proposed as having the best correlation with adverse cardiovascular outcomes (reference). Unfortunately, the accuracy of LDLC or LDL particle number measurements is currently not monitored by national standardization programs. Direct comparisons between the various testing methods have been limited limiting our ability to accurately interpret and compare values across vendors and lipid parameters. Hypothesis: * LDL particle count numbers determined by NMR (Liposcience) provides the best estimates of cardiovascular risk * Discrepancies exist between the LDL particle count by NMR and other values: * Calculated LDLC * Directly measured LDL (VAP and ion mobility) Objective: * To determine the test which has the highest concordance and lowest concordance with the NMR test Study Design * Prospective analysis with a target study population of 100 patients * Superiority study aimed to detect a 300 point difference in LDL particle count * Requires a one-time lab draw for all patients Inclusion criteria * Greater than 18 years of age * On statin, statin and natural supplements, or natural supplements only Exclusion criteria * Within 6 months from an acute myocardial infarction (MI) or acute coronary syndrome (ACS) * Non-English speaker Risks to the patient: * Loss of personal health information * Phlebotomy related risks, including injury, bruising, and vasovagal reactions