Weekly collections over 6 to 8 weeks are likely to ascertain the peaks and troughs of physiological fluctuation of most clinical pathology parameters. Collections over shorter or longer time intervals may be subject to a variety of biases or changes in health status. Weekly collections from a minimum of 10-15 study subjects over a minimum of 4-6 weeks are recommended as a minimum since these result in appropriate power for the most studies.¹ For some circumstances or measurands, shorter or longer collection intervals may of interest or all that practicality allows (eg zoo animals that need to be sedated for sampling), however, the numbers of collections and duration of studies should be justified.

The collection schedule and conditions should be reported, including the site of collection and time period between collections. The conditions of collection should include the type of specimen (serum, plasma, urine, cerebrospinal fluid, whole venous blood, whole arterial blood, etc.) site of collection (jugular vein, saphenous vein, cephalic vein, ear vein, capillary, facial artery, etc.), collection tube (manufacturer, additives [if any], and type and size of tube), number[s] of collectors, and collection method (tourniquet, manual vascular compression, other). These conditions should be standardized as should the time of day of collection, order of collection (animal order, tube order). Any special considerations based on species or environment should be reported. Because of recent data indicating possible seasonal variations in some routine measurands2 and known effects of season on some species (some birds,³ some wildlife,⁴ horses), the month(s) over which the study was conducted and the hemisphere (northern, southern), latitude and altitude should be included.

The handling of the specimens between collection and analysis should be reported. This should include the transport time and condition of the samples, whether or not they are frozen and the temperature at which they are frozen, any modifications or processing prior to analysis and time period of storage prior to analysis. In order to minimize variation associated with analyses conducted on different days, operators and other factors that may vary day-to-day, specimens that are stable with freezing should be frozen and analyzed as a single or several small batches. If specimen stability is an issue and freezing is not possible, such as with hematology samples, then specimens should be analyzed within a standardized time period relative to collection, taking into consideration the stability of the measurands.

1. Røraas T, Petersen PH, Sandberg S. CIs and power calculations for wi thin-person biological variation: effect of analytical imprecision, number of replicates, number of samples, and number of individuals. Clin Chem. 2012. 1877-1881.

2. Schreiber CM, Stewart AJ, Kwessi E, et al. Seasonal variation in results of diagnostic tests for pituitary pars intermedia dysfunction in older, clinically normal geldings. J Am Vet Med Assoc 2012; 241-248.

3. Scope A, Frommlet F, Schwendenwein I. Circadian and seasonal variability and influence of sex and race on eight clinical chemistry parameters in budgerigars (Melopsittacus undulatus, Shaw 1805). Res Vet Sci 2005;78:85-91.

4. Scope A, Schwendenwein I, Schauberger G. Characterization and quantification of the influence of season and gender on plasma chemistries of Hermann’s tortoises (Testudo hermanni, Gmelin 1789). Res Vet Sci 2013; 95:59-68.