Objective: To evaluate changes in stability of haptoglobin and C-reactive protein (CRP) concentrations caused by freezing of saliva and meat juice samples.
Animals: 16 specific-pathogen-free pigs and 16 pigs with clinical signs of disease.
Procedures: Saliva and diaphragmatic muscle were collected immediately before and after slaughter, respectively. Haptoglobin and CRP concentrations of pooled samples were measured before storage (day 0) and after 7, 15, 30, 60, 120, 210, and 365 days of storage at -20°C and after repeated freezing-thawing cycles (up to 7 times). In a second experiment, addition of a protease-inhibitor cocktail to saliva and storage of saliva samples at -80°C for up to 30 days were assessed for effects on CRP concentrations.
Results: Haptoglobin concentrations in saliva did not change for up to 120 days in samples stored at -20°C, but longer storage times and multiple freezing-thawing cycles increased haptoglobin concentrations. Salivary CRP concentrations decreased significantly after 7 days of storage at -20°C, and addition of a protease-inhibitor cocktail did not improve CRP stability. Lower temperatures limited salivary CRP degradation. In meat juice, haptoglobin and CRP concentrations were stable at -20°C up to 210 days.
Conclusions and clinical relevance: Acute-phase protein measurements in saliva should be performed as soon as possible after sample collection. When this is not possible, storage temperature of -80°C is recommended. Acute-phase protein concentrations appeared to be more stable in meat juice samples than in saliva samples. Saliva and meat juice could be used as alternatives to serum for haptoglobin and CRP analysis.