196 C oronary heart disease (CHD) is the leading cause of death in the United States, and yet disease risk assess- ment remains inadequate. The current practice of using lipid levels to evaluate the likelihood of future CHD has proven moderately effective in determining patient risk; however, tens of thousands of individuals with normal cholesterol experience CHD events every year. 1 To improve risk assess- ment, measurements of lipid and nonlipid biomarkers have been suggested, including lipoprotein (a), C-reactive protein, homocysteine, and lipoprotein subfraction analysis. Among these assays, low-density lipoprotein subfraction analysis has shown notable potential, particularly the quantification of small dense low-density lipoprotein (sdLDL) particles. Previous studies have shown that sdLDL particle concentra- tions are higher in cases of incident coronary artery disease, 2 myocardial infarction, 3 stroke, 4 and overall cardiovascular disease (CVD). 5 Moreover, sdLDL levels have been shown to correlate with CHD more strongly than LDL-C and large LDL particle concentrations across multiple prospective and case– control studies 5–8 although not all. 9–11 Until recently, practical considerations made routine measurement of sdLDL in a clini- cal laboratory setting unfeasible. Methods such as ultracentrifu- gation, nuclear magnetic resonance (NMR) spectroscopy, and gradient gel electrophoresis require the use of laboratory equip- ment that may be unavailable or cost prohibitive. In contrast, a newly developed assay that measures a surrogate of sdLDL par- ticles, sdLDL cholesterol content (sdLDL-C), uses automated and readily available clinical laboratory instrumentation. 12 Thus far, only a limited number of studies have evaluated the efficacy of sdLDL-C measurement, and no studies have © 2013 American Heart Association, Inc. Arterioscler Thromb Vasc Biol is available at http://atvb.ahajournals.org DOI: 10.1161/ATVBAHA.113.302401 Objective—Coronary heart disease (CHD) is the leading cause of death in the United States, yet assessing risk of its development remains challenging. The present study evaluates a new automated assay of small dense low-density lipoprotein cholesterol content (sdLDL-C) and whether sdLDL-C is a risk factor for CHD compared with LDL-C or small LDL particle concentrations derived from nuclear magnetic resonance spectroscopy. Approach and Results—sdLDL-C was measured using a new automated enzymatic method, and small LDL concentrations were obtained by nuclear magnetic resonance in 4387 Multi-Ethnic Study of Atherosclerosis participants. Cox regression analysis estimated hazard ratios for developing CHD for 8.5 years after adjustments for age, race, sex, systolic blood pressure, hypertension medication use, high-density lipoprotein cholesterol, and triglycerides. Elevated sdLDL-C was a risk factor for CHD in normoglycemic individuals. Those in the top sdLDL-C quartile showed higher risk of incident CHD (hazard ratio, 2.41; P=0.0037) compared with those in the bottom quartile and indicated greater CHD risk than the corresponding quartile of LDL-C (hazard ratio, 1.75; P=0.019). The association of sdLDL-C with CHD risk remained significant when LDL-C (<2.57 mmol/L) was included in a multivariate model (hazard ratio, 2.37; P=0.012). Nuclear magnetic resonance–derived small LDL concentrations did not convey a significant risk of CHD. Those with impaired fasting glucose or diabetes mellitus showed higher sdLDL-C and small LDL concentrations but neither was associated with higher CHD risk in these individuals. Conclusions—This new automated method for sdLDL-C identifies risk for CHD that would remain undetected using standard lipid measures, but only in normoglycemic, nondiabetic individuals. (Arterioscler Thromb Vasc Biol. 2014;34:196-201.) Key Words: coronary disease Received on: July 3, 2013; final version accepted on: October 30, 2013. From the Department of Laboratory Medicine and Pathology (M.Y.T., B.T.S.) and Division of Biostatistics (W.G.), University of Minnesota School of Public Health, Minneapolis, MN; Department of Biostatistics, University of Washington, Seattle, WA (R.L.M.); Health Diagnostic Laboratory, Inc, Richmond, VA (R.W., J.M., D.M.H.); and National Institutes of Health Molecular Disease Branch, National Heart, Lung, and Blood Institute, Bethesda, MD (A.T.R.). The online-only Data Supplement is available with this article at http://atvb.ahajournals.org/lookup/suppl/doi:10.1161/ATVBAHA.113.302401/-/DC1. Correspondence to Michael Y. Tsai, Department of Laboratory Medicine and Pathology, University of Minnesota School of Public Health, 420 Delaware St SE, Mayo Mail Code 609, Minneapolis, MN 55455-0392. E-mail tsaix001@umn.edu New Automated Assay of Small Dense Low-Density Lipoprotein Cholesterol Identifies Risk of Coronary Heart Disease The Multi-Ethnic Study of Atherosclerosis Michael Y. Tsai, Brian T. Steffen, Weihua Guan, Robyn L. McClelland, Russell Warnick, Joseph McConnell, Daniel M. Hoefner, Alan T. Remaley Clinical and Population Studies Downloaded from http://ahajournals.org by on June 18, 2020