title: Estimation of the low-density lipoprotein (LDL) subclass phenotype using a direct, automated assay of small dense LDL-cholesterol without sample pretreatment.
abstract: BACKGROUND
  A new method (sLDL-EX "SEIKEN") is commercially available for the direct quantification of small dense LDL-cholesterol (sd-LDL) on automated chemistry analyzers, without manual sample pretreatment. We evaluated the performance of this direct assay to estimate the small dense LDL subclass phenotype ("non-A"), defined by polyacrylamide gel tube electrophoresis.
  
  
  METHODS
  Fasting serum samples from 189 healthy subjects (age 18-75y, 96 females) were collected. The direct sd-LDL assay (from Randox Laboratories) was applied on a Roche Modular P analyzer. The Quantimetrix Lipoprint(TM) LDL System was used to define LDL subclass phenotypes (A and non-A). ROC curve analysis was performed for sd-LDL and other lipids and apolipoproteins (apo) with respect to phenotype non-A.
  
  
  RESULTS
  sd-LDL concentrations (40.4+/-18.6mg/dl) in the total group correlated (P<0.0001) with apoB (r=0.831), apoB/A-I ratio (r=0.757), non-HDL-cholesterol (r=0.821), triglycerides (r=0.439), and LDL-cholesterol (r=0.641). Higher sd-LDL concentrations (P<0.0001) were measured in subjects with LDL phenotype non-A (53.6+/-17.0mg/dl, n=92) than in those with phenotype A (27.9+/-8.9mg/dl, n=97). In logistic regression analysis, sd-LDL and apoA-I were independently associated with LDL subclass phenotype non-A. Highest areas under ROC curves were obtained for sd-LDL (0.943), triglycerides (0.833), triglyceride/HDL-cholesterol (0.838) and apoB/A-I ratio (0.826) to predict phenotype non-A. The sd-LDL cut-off point for optimal sensitivity (87.9%) and specificity (92.8%) was >38.5mg/dl.
  
  
  CONCLUSIONS
  The direct, homogeneous sd-LDL method is easily applicable on an automated chemistry analyzer and shows acceptable performance to estimate the electrophoretic LDL subclass phenotype.
authors.affiliation: Department of Laboratory Medicine, AZ St-Jan Hospital, Bruges, Belgium.
authors.forename: Annemie
authors.initials: A
authors.lastname: Vandermeersch
authors.forename: Sara
authors.initials: S
authors.lastname: Ameye
authors.forename: Dieter
authors.initials: D
authors.lastname: Puype
authors.forename: Dominique
authors.initials: D
authors.lastname: Petitjean
authors.forename: Marc
authors.initials: M
authors.lastname: De Buyzere
authors.forename: Michel R
authors.initials: MR
authors.lastname: Langlois
mesh_terms: D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D008077:Lipoproteins, LDL / Q000145:classification*; D015203:Reproducibility of Results; D014280:Triglycerides / Q000097:blood
chemical_list: D008077:Lipoproteins, LDL; D014280:Triglycerides