title: Comparison of LDL cholesterol concentrations by Friedewald calculation and direct measurement in relation to cardiovascular events in 27,331 women.
abstract: BACKGROUND
  National Cholesterol Education Program (NCEP) guidelines recommend development of direct assays for LDL cholesterol (LDL-C) measurement, but it is unclear how these assays compare with Friedewald calculation in predicting cardiovascular disease (CVD).
  
  
  METHODS
  In a study of 27 331 healthy women with triglycerides <or=4.52 mmol/L (<or=400 mg/dL), baseline fasting Friedewald LDL-C was compared with fasting and nonfasting direct homogenous measurement for incident CVD during an 11-year period.
  
  
  RESULTS
  Fasting LDL-C measurements obtained by the 2 methods were highly correlated (r = 0.976, P < 0.001). Compared with fasting Friedewald LDL-C, mean fasting direct LDL-C was 0.15 mmol/L (5.6 mg/dL) lower and nonfasting direct LDL-C 0.30 mmol/L (11.5 mg/dL) lower, both P < 0.0001. The adjusted hazard ratio per 1-SD increment was 1.23 [95% CI 1.15-1.32; 1-SD 0.88 mmol/L (34.1 mg/dL)] for fasting direct LDL-C and 1.22 [95% CI 1.14-1.30; 1-SD 0.90 mmol/L (34.9 mg/dL)] for fasting Friedewald. Nonfasting LDL-C was not associated with CVD by either method. Fasting LDL-C measurements fell into the same NCEP risk category with either method for 79.3% of participants, whereas they differed by 1 NCEP category for 20.7% of participants, with most classified into a lower-risk category by direct LDL-C.
  
  
  CONCLUSIONS
  The association of LDL-C with CVD by the 2 methods was nearly identical in fasting samples. However, the lower direct LDL-C concentrations may misclassify many individuals into a lower NCEP category. Moreover, the lack of association of nonfasting direct LDL-C with CVD raises questions regarding the clinical utility of a direct assay for LDL-C in nonfasting blood samples.
authors.affiliation: Division of Preventive Medicine, Donald W Reynolds Center for Cardiovascular Research, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02215, USA. smora@partners.org
authors.forename: Samia
authors.initials: S
authors.lastname: Mora
authors.forename: Nader
authors.initials: N
authors.lastname: Rifai
authors.forename: Julie E
authors.initials: JE
authors.lastname: Buring
authors.forename: Paul M
authors.initials: PM
authors.lastname: Ridker
mesh_terms: D001241:Aspirin / Q000008:administration & dosage; D002318:Cardiovascular Diseases / Q000097:blood / Q000517:prevention & control; D008078:Cholesterol, LDL / Q000097:blood*; D015331:Cohort Studies; D005215:Fasting / Q000097:blood*; D005260:Female; D006801:Humans; D006937:Hypercholesterolemia / Q000097:blood; D008875:Middle Aged; D011237:Predictive Value of Tests; D011446:Prospective Studies; D016032:Randomized Controlled Trials as Topic; D018709:Statistics, Nonparametric; D014280:Triglycerides / Q000097:blood; D014810:Vitamin E / Q000008:administration & dosage
chemical_list: D008078:Cholesterol, LDL; D014280:Triglycerides; D014810:Vitamin E; D001241:Aspirin