Biological variation of serum canine calprotectin concentrations as measured by ELISA in healthy dogs.

Calprotectin is a useful biomarker of inflammation in dogs. However, the biological variation of serum canine calprotectin is unknown. Indices of biological variation were determined in serial serum samples (n=147) from 11 healthy dogs (males/females: 4/7, median age: 5 years): analytical (3.0%), intra-individual (29.9%), and inter-individual variation (33.2%), reciprocal index of individuality (1.1), and index of heterogeneity (4.9). Serum calprotectin concentrations measured by ELISA and by the previous radioimmunoassay were highly correlated, but a constant and proportional bias exists between both assays. A de novo ELISA-reference interval (RI) for serum calprotectin concentration was established (0.6-11.8mg/L). Moderate changes in serum calprotectin (minimum critical difference: 6.4mg/L) between sequential measurements are needed to be considered relevant, and a population-based RI may or may not be appropriate for serum calprotectin.