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 (CV G and CV I ) 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, CV G was 90.8%, CV I was 115.5%, and the analytical variability (CV A ) was 6.3%; the index of individuality was 0.78, and 1-sided critical difference was 269. 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.

Many frequently measured analytes included in routine serum biochemical panels have high individuality. Thus, use of standard reference intervals to monitor changes over time in an individual is likely to miss meaningful biological change.

No abstract

Background: Biologic variation of biochemical analytes, both within individuals and between individuals, determines whether population-based reference intervals (RIs) are appropriate when interpreting if a particular change is clinically relevant for a specific individual. Objectives: We aimed to evaluate the biologic variation of symmetric dimethylarginine (SDMA) in clinically healthy cats. Methods: A prospective, observational study was performed in which 10 clinically healthy, client-owned cats were sampled for serum biochemical analyses once weekly for 6 weeks. Serum samples were frozen, and then single batches were analyzed for SDMA, using both liquid chromatography-mass spectroscopy (LC-MS), and an enzyme multiplied immunoassay technique (EMIT), and creatinine by modified Jaffe method. Restricted maximum likelihood estimations were used to determine the coefficients of variation (CVs) describing variation within each cat, between cats, and the analytical variation. These CVs were used to determine the indices of individuality and reference change values (RCVs). Results: SDMA had an intermediate index of individuality that could be evaluated by both RCV and population-based RIs. In contrast, creatinine had a high index of individuality best evaluated with RCVs. Serum SDMA concentrations evaluated with either the reference standard, LC-MS, or the clinically used EMIT yielded similar results. Conclusions: Clinicians should consider biologic variation when selecting the best method for interpreting changes in biochemical analytes. Specifically, establishing each cat's baseline serum creatinine and SDMA concentrations during health, and applying RCVs to subsequent measurements could improve the recognition of meaningful biologic changes.