title: Identifying patients with hypercholesterolemia. More than one blood sample is needed.
abstract: OBJECTIVE
  To compare the use of one and two blood samples for diagnosing hypercholesterolemia
  
  
  METHODS
  A test-retest substudy conducted as part of a randomized control trial designed to compare the effectiveness of different counseling strategies for lowering serum cholesterol, dietary fat, and dietary cholesterol in patients with moderate hypercholesterolemia.
  
  
  METHODS
  Thirty urban family practices.
  
  
  METHODS
  One hundred forty-two patients provided two blood samples for total cholesterol (TC) level determination at two different times (test results were being used as an eligibility criterion for enrollment in the main trial).
  
  
  METHODS
  Number of subjects correctly classified to cholesterol risk category (normal < 6.2 mmol/L; moderate 6.2 to 6.9 mmol/L; high > 6.9 mmol/L) on the basis of one TC value and on the average of two TC values.
  
  
  RESULTS
  Overall misclassification rate on initial TC level was 22.5%. Overall false-positive rate was 19.0%, but false-positive rate for those initially assigned to the high category was 50%. Overall false-negative rate was 3.5%. Misclassification rates did not differ statistically on the basis of age, sex, blood pressure, smoking status, family history of coronary heart disease, presence of diabetes, obesity, the laboratory used, or whether the patient had fasted before giving blood.
  
  
  CONCLUSIONS
  Single TC levels are too unreliable for diagnostic purposes, even if the subjects fast before testing. Family physicians should base their treatment decisions on the average of two cholesterol readings taken at different times 1 to 8 weeks apart.
authors.affiliation: Department of Physical Therapy, Faculty of Applied Health Sciences, University of Western Ontario, London.
authors.forename: M
authors.initials: M
authors.lastname: Speechley
authors.forename: S
authors.initials: S
authors.lastname: McNair
authors.forename: A
authors.initials: A
authors.lastname: Leffley
authors.forename: M
authors.initials: M
authors.lastname: Bass
mesh_terms: D000328:Adult; D000368:Aged; D002784:Cholesterol / Q000097:blood*; D004032:Diet; D005260:Female; D006801:Humans; D006937:Hypercholesterolemia / Q000097:blood / Q000175:diagnosis*; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D015203:Reproducibility of Results
chemical_list: D002784:Cholesterol