Use of Fourier-transform infrared spectroscopy for the diagnosis of failure of transfer of passive immunity and measurement of immunoglobulin concentrations in horses.

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.

Laminar fluid diffusion interface preconditioning of serum and urine for reagent-free infrared clinical analysis and diagnostics.

A number of reagent-free infrared spectroscopic diagnostic and analytical methods have been established previously making use of dry biofluid films. For example, this approach has successfully measured high concentration analytes of serum and urine. However, a number of low concentration diagnostically relevant analytes presently elude detection by infrared spectroscopy. This is due in part to their relatively low concentration and in part to spectral interference by other strongly absorbing constituents. The applicability of the technique would be broadened substantially if it were possible to concentrate and separate lower concentration analytes, e. g., serum creatinine and urine proteins, from the obscuring presence of relatively high concentration compounds. One possible means to achieve this is through microfluidic sample preconditioning based on laminar fluid diffusion interfaces. The objective of this study was therefore to qualitatively assess the performance of this technology in preferentially separating certain serum and urine analytes of clinical interest that presently lie just below the threshold of detection by infrared spectroscopy. Observations from simulated and genuine urine and serum samples strongly suggest that this process should improve existing accuracy and extend the range of detectable analytes.