Internal Medicine Resident Colorado State University Fort Collins, Colorado, United States
Abstract: Background – C-reactive protein (CPR) serum concentrations are used to monitor systemic inflammatory disease syndromes. There are multiple methods of measuring CRP but no clear consensus on the optimal assay. CRP concentrations are believed to degrade even if sera are frozen, impacting retrospective studies.
Objectives – This study was intended to assess for degradation of CRP when stored at -80° C and to compare the results of three different commercially available CRP assays.
Animals – Sera (n = 19) collected from research beagles in other experiments with IACUC approval.
Methods – The 19 sera were originally assayed with a commercially available ELISA (Abcam - canine). The sera were stored for approximately 14 weeks at -80° C until assayed in this study. After thawing at room temperature, the sera were re-assayed in the ELISA and 2 other assays (Randox Canine CRP and Gentian CRP-G).
Results – Of 19 samples re-tested in the same ELISA after storage at -80° C, 18 showed increased CRP concentrations, with changes ranging from 24 to 2000% (Median = 43%.) While the Abcam and Gentian assays detected CRP in all 19 samples, 7 samples were negative in the Randox assay. CRP detection rates were similar in the Abcam (100%), Randox (83.3%) and Gentian (100%) assays using the 6 samples most likely to show inflammation.
Conclusions and clinical importance – If CRP measurement is used in management of clinical cases, the assay used in serial monitoring should be consistent. Using the Abcam kit, CRP concentrations generally increased after storage rather than decreased as expected.
