title: Comparison of IgG concentrations by radial immunodiffusion, electrophoretic gamma globulin concentrations and total globulins in neonatal foals.
abstract: BACKGROUND
  Failure of transfer of passive immunity (FTPI) in foals is associated with a risk of infection and death. The current diagnostic gold standard is quantification of immunoglobulins using radial immunodiffusion (IgG-RID). Routine diagnosis is often performed using semi-quantitative tests. Concentrations of serum electrophoretic gamma globulins (EGG) and total globulins may be useful to assess FTPI, but few studies have investigated their use.
  
  
  OBJECTIVE
  To assess agreement between IgG-RID and EGG and evaluate the accuracy of total globulin concentration to diagnose FTPI based on both IgG-RID and EGG.
  
  
  METHODS
  Prospective study.
  
  
  METHODS
  A total of 360 serum samples were harvested at 6-24 h post natum from 60 German Warmblood foals. Concentrations of EGG, IgG-RID and total globulin (calculated from total proteins and albumin) were measured. Agreement between EGG and IgG-RID was assessed using Bland-Altman plots and Passing-Bablok regression. The accuracy of total globulin concentration was assessed using rank correlation and ROC curve analysis.
  
  
  RESULTS
  Good agreement was found with slightly lower EGG than IgG-RID concentrations (Bland-Altman systemic bias -1.9 g/l) which was more pronounced at higher concentrations (regression equation: IgG-RID = -0.78 + 1.28 × EGG). Correlations between total globulin concentration and EGG and total globulin concentration and IgG-RID were 0.93 and 0.79, respectively. The area under the curve was 0.982 and 0.952 for EGG <4 and <8 g/l and 0.953 and 0.899 for IgG-RID <4 and <8 g/l. Sensitivities and specificities of total globulin concentration in the diagnosis of FTPI were comparable to those of commonly used screening tests, but cut-offs could be selected to achieve sensitivities of >95% with 71.2% (IgG-RID) and 90.5% (EGG) specificity for <4 g/l and >90% with 66.0% (IgG-RID) and 87.9% (EGG) specificity for <8 g/l.
  
  
  CONCLUSIONS
  There is good agreement between EGG and IgG-RID, with slightly more conservative estimates of immunoglobulins obtained using EGG. Total globulins may be a useful and economic quantitative screening test with cut-offs achieving high sensitivities, but analyser-specific cut-offs may be necessary.
authors.affiliation: Equine Veterinary Clinic Destedt, Germany.
authors.forename: L
authors.initials: L
authors.lastname: Tscheschlok
authors.affiliation: Equine Veterinary Clinic Destedt, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Venner
authors.affiliation: Clinical Diagnostic Laboratory, Department of Clinical Veterinary Medicine, Vetsuisse Faculty, University of Bern, Switzerland.
authors.forename: J
authors.initials: J
authors.lastname: Howard
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D004586:Electrophoresis / Q000379:methods / Q000662:veterinary*; D005260:Female; D006736:Horses / Q000097:blood*; D005779:Immunodiffusion / Q000379:methods / Q000662:veterinary*; D007074:Immunoglobulin G / Q000097:blood*; D008297:Male; D011446:Prospective Studies
chemical_list: D007074:Immunoglobulin G
keywords: IgG; electrophoresis; foal; globulins; horse; radial immunodiffusion