Studies of C-reactive protein stability with freezing and its usefulness in selected diseases in dogs

Objective: Experiment 1 assessed the stability of C-reactive protein (CRP) when stored at -80 °C and compared the results of 3 commercially available CRP assays. For experiment 2, 2 assays were used to assess CRP during infection and treatment of experimental hemoparasite and H3N2 influenza infections. We predicted CRP would degrade with prolonged storage and that it would trend with clinical markers of disease and inflammation in the experimentally infected dogs. Methods: Archived serum from dogs with inflammation caused by experimentally induced hypovolemia was assayed using the Abcam canine CRP ELISA, stored for 14 weeks at -80 °C, and reanalyzed via ELISA and 2 other CRP assays (Randox and Gentian). Archived sera from dogs experimentally infected with Babesia gibsoni and Candidatus Mycoplasma hematoparvum or H3N2 were evaluated using the ELISA and Gentian assays to assess changes in CRP concentration during clinical progression and resolution of these diseases. Results: C-reactive protein values increased by an average of 3.58 mg/L after storage for 14 weeks. Results from the 3 assays were not analytically equivalent. C-reactive protein values trended inversely with platelet count and Hct in 4 dogs with hemoparasites and were significantly lower in 4 dogs vaccinated with H3N2 compared to 4 nonvaccinated dogs. Conclusions: When monitoring clinical cases, the CRP assay used should be consistent, as a decreased result following freeze-thaw does not occur when stored at -80 °C, and dogs with clinical signs of H3N2 infection have increases in CRP concentrations. Clinical Relevance: This study provides evidence that CRP can be used to monitor some infectious diseases that induce inflammation.