Impact of long-term storage on mid-infrared spectral patterns of serum and synovial fluid samples of dogs with osteoarthritis

Abstract The aim of this study was to evaluate the impact of short versus long-term storage on mid-infrared (MIR) spectral patterns of serum and synovial fluid (SF) of dogs with knee osteoarthritis (OA) and controls. Serum (52 OA and 49 control) and SF (51 OA and 51 control) samples from dogs that had been in short-term (<3 years) frozen state (-80°C) had their MIR spectra obtained. The remaining aliquots were maintained in long-term (>5 years) frozen state before having MIR spectra acquired under the same testing conditions. Spectra from the two time points were significantly different (P<0.0001), however, sample aging accounted for only 1.61% and 2.98% of serum and SF profiles’ variability, respectively. Predictive models for discriminating serum of OA from controls for short-term storage showed 87.3±3.7% sensitivity, 88.9±2.4% specificity and 88.1±2.3% accuracy, while, for long-term storage, values of the same figures of merit were 92.5±2.6%, 97.1±1.7% and 94.8±1.4%, respectively. Predictive models based on short-term stored SF spectra had 97.3±1.6% sensitivity, 89.4±2.6% specificity and 93.4±1.6% accuracy, while the values for long-term storage 95.7±2.1%, 95.7±0.8% and 95.8±1.1%, respectively. Long-term storage of serum and does not significantly alter the performance of predictive algorithms for discriminating OA samples from controls.