title: The optimum number and types of plasma samples necessary for an accurate activated partial thromboplastin time-based heparin therapeutic range.
abstract: BACKGROUND
  Monitoring of unfractionated heparin therapy by activated partial thromboplastin time (aPTT) using the ex vivo method for determining the aPTT-based heparin therapeutic range (HTR) is the standard of practice. Many intrinsic and extrinsic factors influence its accuracy.
  
  
  OBJECTIVE
  To investigate the optimum number and types of samples acceptable for an accurate ex vivo HTR determination.
  
  
  METHODS
  Values from patients receiving unfractionated heparin are used to determine the HTR by published guidelines. The number and types of samples are changed to investigate the effect on HTR parameters.
  
  
  RESULTS
  Absolute minimum number of samples for an accurate HTR is 20, with fewer than 10% of the samples from the same patient or 50% of the samples with international normalized ratio of 1.3 to 1.5.
  
  
  CONCLUSIONS
  The ex vivo HTR method is the best protocol currently available; however, the number of samples used affects its accuracy. The optimum number of samples is 30 or more but the absolute minimum number is 20. In addition, limitation of specific sample types also affects the HTR parameters. An inaccurate HTR may be calculated if inappropriate sample number or types of samples are used.
authors.affiliation: Pathology and Laboratory Medicine Services, Oklahoma City VA Medical Center, Oklahoma City, Oklahoma 73104, USA. Richard-Marlar@ouhsc.edu
authors.forename: Richard A
authors.initials: RA
authors.lastname: Marlar
authors.forename: Jana
authors.initials: J
authors.lastname: Gausman
mesh_terms: D001774:Blood Chemical Analysis; D016903:Drug Monitoring / Q000379:methods* / Q000592:standards / Q000706:statistics & numerical data; D006493:Heparin / Q000008:administration & dosage* / Q000097:blood*; D006801:Humans; D007202:Indicators and Reagents; D019934:International Normalized Ratio; D010314:Partial Thromboplastin Time / Q000379:methods* / Q000592:standards / Q000706:statistics & numerical data; D012015:Reference Standards; D018401:Sample Size; D014859:Warfarin / Q000008:administration & dosage
chemical_list: D007202:Indicators and Reagents; D014859:Warfarin; D006493:Heparin