title: Biological variation of thromboelastrography variables in 10 clinically healthy horses.
abstract: OBJECTIVE
  To assess the utility of population-based reference intervals (PRIs) for interpreting thromboelastography (TEG) variables in horses using biological variation data.
  
  
  METHODS
  Prospective cohort biologic variation study conducted over a 5-week period.
  
  
  METHODS
  Veterinary teaching hospital and research facility.
  
  
  METHODS
  Ten clinically healthy horses randomly selected from a veterinary school research and teaching herd.
  
  
  METHODS
  Horse health was determined using physical examination, CBC, and biochemical and coagulation profiles prior to the start of the study. Subsequently, once weekly blood sampling for TEG testing was performed for 5 weeks.
  
  
  RESULTS
  The 4 TEG variables reaction time (R), clot formation time (K), angle, and maximum amplitude (MA) were measured, and coefficient of variation representing within- and between-horse biological variation (CVi and CVg , respectively) and coefficient of variation representing analytical variation (CVa ) were calculated using a nested ANOVA after removing outlier data. The CVi , CVg , and CVa for R were 26.8%, 5.2%, and 5.9%; for K were 31.0%, 0.0%, and 5.9%; for angle were 9.4%, 6.2%, and 21.7%; and for MA were 3.4%, 4.1%, and 4.4%, respectively. Index of individuality (IOI) was then calculated for each variable using the formula {( CVi² + CVa²/CVg²)}¹/². IOI for R was 5.3, for angle was 3.8, and for MA was 1.4; IOI was not assessed for K.
  
  
  CONCLUSIONS
  PRIs are appropriate for TEG variables, R, angle, and MA when interpreting results from individual horses based on calculated IOI values equal to or greater than 1.4. PRIs are likely appropriate when interpreting K, but IOI could not be calculated for this variable.
authors.affiliation: Departments of Biomedical and Diagnostic Sciences, University of Tennessee, Knoxville, TN, 37996.
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Scruggs
authors.affiliation: Departments of Biomedical and Diagnostic Sciences, University of Tennessee, Knoxville, TN, 37996.
authors.forename: Bente
authors.initials: B
authors.lastname: Flatland
authors.affiliation: Large Animal Clinical Sciences, University of Tennessee, Knoxville, TN, 37996.
authors.forename: Karen A
authors.initials: KA
authors.lastname: McCormick
authors.affiliation: College of Veterinary Medicine and the Office of Information Technology, University of Tennessee, Knoxville, TN, 37996.
authors.forename: Ann
authors.initials: A
authors.lastname: Reed
mesh_terms: D000818:Animals; D001780:Blood Coagulation Tests / Q000379:methods / Q000662:veterinary*; D001800:Blood Specimen Collection; D006736:Horses / Q000097:blood*; D011446:Prospective Studies; D013916:Thrombelastography / Q000662:veterinary*
keywords: coagulation; critical difference; equine; index of individuality; reference change value; viscoelastic analysis