• Biological variation;
  • Critical change value;
  • Diagnostic testing;
  • Inflammatory markers

Background: C-reactive protein (CRP) and specific canine pancreatic lipase immunoreactivity (Spec cPL) are biomarkers of generalized or nonspecific inflammation and pancreatic inflammation in dogs, respectively. The extent of inter- and intraindividual variation over time of these analytes is not well defined in dogs. The minimal critical difference for sequential determinations of these markers (ie, the smallest change necessary to represent physiological change rather than biological variation), has not been defined.

Objectives: To determine the inter- and intraindividual variability (CVG and CVI) and minimal critical difference for sequential determinations of serum CRP and Spec cPL concentrations in apparently healthy dogs.

Animals: Eleven apparently healthy dogs owned by staff or students at a veterinary teaching hospital.

Methods: Blood was collected repeatedly at varying intervals over 12 weeks. CRP and Spec cPL concentrations were determined with commercially available assays. Indices of inter-, intraindividual, and assay variability and 1-sided minimal critical differences for sequential concentrations were calculated.

Results: For CRP, CVG was 90.8%, CVI was 115.5%, and the analytical variability (CVA) was 6.3%; the index of individuality was 0.74, and 1-sided critical difference was 269.9%. For Spec cPL, CVG= 49.48%, CVI= 193.8%, CVA= 8.4%, index of individuality = 0.24, and 1-sided critical difference was 452.6%.

Conclusions and Clinical Importance: A population-based reference range is appropriate for Spec cPL, but questionable for CRP in dogs. Large changes in serial measurements of Spec cPL are necessary to infer clinical importance, more modest changes in CRP are likely to be meaningful.