Serum protein concentrations as predictors of serum immunoglobulin G concentration in neonatal foals

Objective - To determine the predictive value of serum concentrations of total protein (sTP), albumin (sAlb), and globulin (sGlob) measured by automated calorimetric assays to estimate serum immunoglobulin G (sIgG) concentrations in neonatal foals and identify failure of transfer of passive immunity when compared to turbidoimmunometric assay determinations of sIgG. Design - Retrospective and prospective analysis of laboratory data. Setting - University tertiary care facility. Animals - Group 1 (retrospective): foals (n = 45) <= 7 days of age in which sIgG, sGlob, sAlb, and sTP concentrations were measured on an automated chemistry analyzer. Group 2 (prospective): foals (n = 31) <= 7 days of age with same laboratory data collected used to validate equations generated from group 1 foals. Interventions - Spearman rank correlations between measured sIgG and serum protein concentrations were performed. When significant correlation was found, sIgG was estimated using an sGlob simple linear regression and estimated using a sGlob, sTP, and sAlb multiple linear regression. Comparisons between estimated and measured sIgG was performed using Kruskal-Wallis testing. Sensitivity, specificity, positive predictive value, and negative predictive value were calculated to identify foals with sIgG < 8.0 g/L [<800 mg/dL]. Measurements and Main Results - sIgG was correlated with sGlob, sTP, and sAlb (rho = 0.8, 0.6, and 0.3, respectively; P < 0.05). Estimated sIgG and measured sIgG were not different (P > 0.9). In group 1 foals, the sensitivity, specificity, positive predictive value, and negative predictive value were 73%, 76%, 73%, and 83%, respectively, for sGlob, and 90%, 76%, 75%, and 90%, respectively, for multiple proteins estimated sIgG identification of failure of transfer of passive immunity. Test qualities were improved in group 2 foals. Conclusions - Serum protein concentrations may be used to estimate sIgG concentrations in newborn foals. Further investigation using a larger sample size is needed to validate this methodology of assessing humoral immunity in neonatal foals.