title: Within-person variation of plasma homocysteine and effects of posture and tourniquet application.
abstract: BACKGROUND
  Frequently, the result of only a single determination of total homocysteine in plasma (P-Hcy) is used to distinguish between the probability of the presence or absence of risk for vascular disease. A prerequisite for the interpretation of a single P-Hcy test is knowledge of the magnitude of within-person variation and the possible effects of preanalytical variables. However, data on within-person variation are still sparse and inconsistent, and data for the effect on P-Hcy of posture and tourniquet application during venipuncture are not available.
  
  
  METHODS
  The within-person variation of P-Hcy and the effects of posture and tourniquet application during venipuncture were studied in 24 healthy subjects. The analytical imprecision of our stable-isotope dilution assay was 3.1%.
  
  
  RESULTS
  The within-person variation (CV) was 8.1%. Daily supplementation with 0.4 mg of folic acid for 2 weeks produced a small but significant decrease in P-Hcy, but there were no significant changes in within-person variation before and after supplementation. After 30 min in the horizontal posture, P-Hcy declined by 6.3%. A 3-min tourniquet application caused a 2.8% increase of P-Hcy.
  
  
  CONCLUSIONS
  Our value for within-person variation is consistent with results from studies reported recently in the literature. A 3-min tourniquet application does not add appreciable variation to the measurement of P-Hcy, but the posture of the subject during venipuncture contributes considerably to the within-person variation. We recommend that blood collection when the patient is in a supine position be avoided.
authors.affiliation: Department of Clinical Biochemistry, Aarhus University Hospital at Skejby, DK-8000 Aarhus N, Denmark.
authors.forename: K
authors.initials: K
authors.lastname: Rasmussen
authors.forename: J
authors.initials: J
authors.lastname: Moller
authors.forename: M
authors.initials: M
authors.lastname: Lyngbak
mesh_terms: D000328:Adult; D001800:Blood Specimen Collection / Q000295:instrumentation / Q000379:methods; D005260:Female; D005492:Folic Acid; D006710:Homocysteine / Q000097:blood*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011187:Posture; D012307:Risk Factors; D014652:Vascular Diseases / Q000097:blood
chemical_list: D006710:Homocysteine; D005492:Folic Acid