Study on biological variability of five acute-phase reactants in dogs

The analytical, within-dog and between-dog components of variation were estimated for serum iron, plasma fibrinogen, serum C-reactive protein, serum α1-acid glycoprotein and serum haptoglobin, and used to 1) estimate the critical difference for significance between serial results; 2) assess the utility of conventional population-based reference ranges; and 3) set objective analytical performance standards for each quantity. Blood was sampled weekly from eight clinically healthy Beagle dogs for 5 weeks. Results were analysed for outliers and subsequently subjected to nested analysis of variance to obtain the components of variance. All quantities showed a degree of individuality, which can make the use of conventional population-based reference ranges alone an insensitive interpretative criterion. The critical difference needed for significance between serial results makes an objective criterion for monitoring individuals, and are useful for dogs where serial results are available for comparison. Desirable analytical imprecision was met for all quantities except for serum α1-acid glycoprotein, where improvement is warranted. Objective analytical performance standards for inaccuracy and total error were set up for each quantity.