title: A comparative study of four independent methods to measure LDL particle concentration.
abstract: BACKGROUND
  Low-density lipoprotein particle concentration (LDL-P) is generally more predictive of clinical cardiovascular endpoints than LDL cholesterol (LDL-C). Few studies have directly compared multiple LDL-P methods, particularly with ultracentrifugation.
  
  
  OBJECTIVE
  Examine comparability and precision of 4 LDL-P methods.
  
  
  METHODS
  We divided serum from 48 subjects into blinded triplicates and measured LDL-P in 3 separate laboratories by 4 methods: ultracentrifugation (reference method), a novel electrophoretic method, and nuclear magnetic resonance spectroscopy (NMR) by 2 independent methods: a 400 MHz Vantera(®) instrument supplied by Liposcience (LS-NMR) and operated at ARUP Laboratories, and a 600 MHz Bruker instrument (ASCEND 600) operated at Health Diagnostic Laboratory (HD-NMR).
  
  
  RESULTS
  Of the 4 methods, ultracentrifugation was the most precise and LS-NMR the least; the latter had a significantly greater CV (p < 0.0001) as compared with all 3 of the other methods, although all CVs were clinically acceptable. The electrophoretic method showed similar precision to ultracentrifugation, while HD-NMR was intermediate. The HD-NMR had the slope closest to 1 (0.90, 95% CI 0.71 to 1.09) and the intercept closest to 0 (-48, -353 to 256) compared to the ultracentrifugation method in Deming regression models. While the two NMR methods correlated well (r = 0.95) with each other and had a slope equivalent to 1 (1.08, 0.98 to 1.19), their intercept in Deming regression excluded 0 (194, 53 to 335) indicating a vertical shift between the two methods.
  
  
  CONCLUSIONS
  This LDL-P method comparison may prove useful for future research and clinical applications.
authors.affiliation: Cardiovascular Genetics, Cardiovascular Medicine, Department of Internal Medicine, University of Utah, Salt Lake City, UT 84108, USA. Electronic address: paul.hopkins@utah.edu.
authors.forename: Paul N
authors.initials: PN
authors.lastname: Hopkins
authors.affiliation: Department of Internal Medicine, Sanford School of Medicine, University of South Dakota, Sioux Falls, SD 57105, USA; Health Diagnostic Laboratory, Inc., Richmond, VA 23219, USA.
authors.forename: James V
authors.initials: JV
authors.lastname: Pottala
authors.affiliation: Cardiovascular Genetics, Cardiovascular Medicine, Department of Internal Medicine, University of Utah, Salt Lake City, UT 84108, USA.
authors.forename: M Nazeem
authors.initials: MN
authors.lastname: Nanjee
mesh_terms: D001053:Apolipoproteins / Q000737:chemistry; D008078:Cholesterol, LDL / Q000097:blood*; D019411:Clinical Laboratory Techniques / Q000379:methods*; D004586:Electrophoresis; D006801:Humans; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D010316:Particle Size; D012044:Regression Analysis; D015203:Reproducibility of Results; D012307:Risk Factors; D014461:Ultracentrifugation / Q000379:methods*
chemical_list: D001053:Apolipoproteins; D008078:Cholesterol, LDL
keywords: Deming regression; Electrophoresis; LDL particle concentration; Nuclear magnetic resonance spectroscopy; Ultracentrifugation