title: Comparison of refractometers and test endpoints in the measurement of serum protein concentration to assess passive transfer status in calves.
abstract: OBJECTIVE
  To evaluate 3 refractometers for detection of failure of passive transfer (FPT) of immunity in calves, and assess the effect of refractometric test endpoints on sensitivity, specificity, and proportion of calves classified correctly with regard to passive transfer status.
  
  
  METHODS
  Prospective study.
  
  
  METHODS
  90 calves.
  
  
  METHODS
  Blood samples were obtained from calves that were < 10 days old. Serum IgG concentration was determined by use of a radial immunodiffusion assay. Accuracy of 3 refractometers in the prediction of serum IgG concentration was determined by use of standard epidemiologic methods and a linear regression model.
  
  
  RESULTS
  At a serum protein concentration test endpoint of 5.2 g/dL, sensitivity of each refractometer was 0.89 or 0.93, and specificity ranged from 0.80 to 0.91. For all refractometers, serum protein concentration test endpoints of 5.0 or 5.2 g/dL resulted in sensitivity > 0.80, specificity > 0.80, and proportion of calves classified correctly > 0.85. Serum protein concentrations equivalent to 1,000 mg of IgG/dL of serum were 4.9, 4.8, and 5.1 g/dL for the 3 refractometers.
  
  
  CONCLUSIONS
  The refractometers, including a nontemperature-compensating instrument, performed similarly in detection of FPT. Serum protein concentration test endpoints of 5.0 and 5.2 g/dL yielded accurate results in the assessment of adequacy of passive transfer; lower or higher test endpoints misclassified larger numbers of calves.
authors.affiliation: Department of Veterinary Medicine and Surgery, College of Veterinary Medicine, University of Missouri, Columbia, MO 65211, USA.
authors.forename: Christopher D
authors.initials: CD
authors.lastname: Calloway
authors.forename: Jeff W
authors.initials: JW
authors.lastname: Tyler
authors.forename: Ronald K
authors.initials: RK
authors.lastname: Tessman
authors.forename: Douglas
authors.initials: D
authors.lastname: Hostetler
authors.forename: Julie
authors.initials: J
authors.lastname: Holle
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001798:Blood Proteins / Q000032:analysis; D002417:Cattle / Q000097:blood* / Q000276:immunology; D005260:Female; D007112:Immunity, Maternally-Acquired; D005779:Immunodiffusion / Q000662:veterinary; D007074:Immunoglobulin G / Q000097:blood*; D011446:Prospective Studies; D012031:Refractometry / Q000295:instrumentation / Q000379:methods / Q000662:veterinary*; D012044:Regression Analysis; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D001798:Blood Proteins; D007074:Immunoglobulin G