Comparison of IgG concentrations by radial immunodiffusion, electrophoretic gamma globulin concentrations and total globulins in neonatal foals.

Abstract

REASONS FOR PERFORMING STUDY: 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. OBJECTIVES: 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. STUDY DESIGN: 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 &#xd7; 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.