Serum paraoxonase 1 activity in dogs : preanalytical and analytical factors and correlation with C-reactive protein and alpha-2-globulin

Background: Serum activity of paraoxonase (PON1) decreases during inflammation in many species. Little information is available on paraoxon-based tests and the possible role of PON1 in dogs. Objectives: The objectives of the study were to validate an automated paraoxon-based assay to measure PON1 activity in canine serum, to determine its stability under different storage conditions, to determine a reference interval (RI) in healthy dogs, and to assess whether PON1 is of comparable diagnostic value as C-reactive protein (CRP) and α2-globulins. Methods: Intra-assay and inter-assay imprecision, linearity under dilution (LUD), interference, and storage artifacts were evaluated. A PON1 RI was determined for healthy dogs, and PON1 activity, sensitivity, and specificity were compared with CRP and α2-globulins. Results: Intra- and inter-assay CVs were below 1.6% and 7.8%, respectively. The LUD test fitted the linear model. PON1 activity measurements were increased after addition of hemolysates and lipids, and after storage for 12 hours at room temperature, 72 hours at 4°C, and 6 months at -20°C. PON1 activity and CRP or α2-globulins did not correlate well. PON1 activity decreased significantly only in dogs with very high CRP concentrations. In contrast to CRP and α2-globulins, PON1 activity was not significantly different between dogs with and without inflammation. Conclusions: The automated paraoxon-based method to assess serum canine PON1 activity was accurate and precise, but it was influenced by hemolysis, lipemia, and standard storage conditions. In this study, contrarily to CRP and α2-globulins, PON1 activity did not provide diagnostic value as a negative acute phase protein in dogs.