Knowledge of biological variation is important, as it can impact medical care, particularly with the increasing use of “senior panels;” however, it is not routinely investigated in dogs. It is assumed that early detection of abnormalities will allow early intervention and treatment. In this prospective study, blood from 11 pet dogs (median age, 5 years [range, 1–9 years]) was collected q24h for 7 days, q1wk for 6 weeks, and again at 3 months. The most commonly evaluated serum biochemistry tests were analyzed and samples were stored at -80°C until analysis. Statistical analyses revealed high individuality for many of the 14 biochemistry analytes tested. Investigators concluded that standard reference intervals to monitor changes over time in an individual were likely to miss meaningful biochemical changes.

Commentary
Biological variation concerns veterinarians every day. In this study, biochemical values were analyzed at multiple time points in healthy dogs; published reference ranges were statistically inadequate for encompassing individual variance. One could simply distrust most published reference ranges when interpreting individual values, or one could be suspicious when suspicion is due. Error, be it technical or the result of a random population bias, exists. If a value is mildly low or high for the reference range and there is some biological leeway before the worst is assumed, then there is room for debating relevance. Alternatively, if a value is low normal or high normal but there is an overwhelming clinical foreboding, it may be good to trust instinct. This article addressed a commonplace problem of poorly fitting test results; however, the medical disasters nested comfortably within the reference range are rare. We must always be shrewd and attentive when concerned.—Ewan Wolff, DVM

Source
Estimates of biological variation in routinely measured biochemical analytes in clinically healthy dogs. Ruaux CG, Carney PC, Suchodolski JS, Steiner JM. VET CLIN PATHOL 41:541-547, 2012.