Synovial Fluid C-Reactive Protein as a Biomarker in Osteoarthritis, Immune-Mediated Polyarthritis and Bacterial Infective Arthritis

This study aimed to explore the diagnostic utility of synovial fluid C-reactive protein (CRP) concentrations as a biomarker for discrimination between osteoarthritis, immune-mediated polyarthritis (IMPA) and bacterial infective arthritis and to determine correlations between synovial CRP concentrations with synovial neutrophil cell counts, disease severity and clinical outcome.Synovial fluid was collected prospectively from dogs presenting with osteoarthritis, IMPA or bacterial infective arthritis (11 dogs in each group). An enzyme-linked immunosorbent assay was used to measure CRP in synovial fluid and serum. Other data collected included signalment and clinicopathological findings.Synovial CRP concentrations were significantly lower in the osteoarthritis group versus the IMPA or bacterial infective arthritis groups. There was no significant difference in synovial CRP levels between the bacterial infective and IMPA groups. Serum CRP was positively associated with synovial CRP in IMPA cases. In the IMPA and bacterial infective arthritis groups, synovial neutrophil count was positively associated with synovial CRP concentration. Lameness severity was positively associated with synovial CRP concentration in the bacterial infective and osteoarthritis groups.Measurement of synovial CRP did not differentiate between bacterial infective arthritis cases and IMPA cases in this cohort of dogs, but it is useful in differentiating between inflammatory and non-inflammatory arthropathies.