Use of Fourier-Transform Infrared Spectroscopy for the Diagnosis of Failure of Transfer of Passive Immunity and Measurement of Immunoglobulin Concentrations in Horses

Abstract

Background: The economic, accurate, and rapid screening of foals for failure of transfer of passive immunity (FPT) is essential to ensure timely intervention. Hypothesis: Infrared (IR) spectroscopy of foal sera and pattern recognition may be used to diagnose FPT and quantify serum IgG. Samples: Sera from 194 foals (24–72 hours) with serum immunoglobulin G (IgG) concentrations determined previously by radial immunodiffusion assay (RID) were used. Methods: IR spectra were recorded for the serum samples, and the data were randomly divided into training and independent test sets, each containing both FPT-positive (IgG <400 mg/dL) and non-FPT samples. A genetic optimal region selection algorithm and linear discriminant analysis were used to partition the training spectra, and the resulting classifier was then validated by comparing the IR-predicted FPT status for each of the test samples to that provided by the RID IgG assay. A quantitative IR-based assay for IgG was developed using partial least squares (PLS) and validated by testing its ability to predict IgG concentrations. Results: Specificity, sensitivity, and accuracy for the combined data were 92.5, 96.8, and 95.9%, respectively. Corresponding positive (88.1%) and negative predictive (98.0%) values determined a success rate of 95–97% as compared to RID-based IgG concentrations. The IR-based quantitative assay yielded correlation coefficients for IR spectroscopy versus RID-based IgG concentrations of 0.90 and 0.86 for the training and test sets, respectively. Conclusions and Clinical Importance: The overall performance of the IR-based test was similar to that of the colorimetric assay and was superior and more economic than other available tests.