How Insensitive Are Population-Based Reference Intervals for Monitoring Hematologic Changes in Asian Elephants (Elephas maximus)?
2018 Joint EAZWV/AAZV/Leibniz-IZW Conference
Kathryn L. Perrin1,2*, BVetMed; Annemarie T. Kristensen2, DVM, PhD, DACVIM-SA, DECVIM-CA & Oncology; Mads F. Bertelsen1, DVM, DVSc, DACZM, D(ECZM); Charlie Gray3; Mads Kjelgaard-Hansen2,4, DVM, PhD
1Center for Zoo and Wild Animal Health, Copenhagen Zoo, Frederiksberg, Denmark; 2Department of Veterinary Clinical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg, Denmark; 3African Lion Safari, Cambridge, Ontario, Canada; 4Global Research, Novo Nordisk, Maaloev, Denmark


Veterinary medicine relies heavily on population-derived reference intervals (popRI) for diagnostic interpretation of clinical pathology parameters. The width of popRI originates from variation around a physiological set-point within each individual (intra-individual variation) as well as the variation between individuals (inter-individual variation), and dedicated investigation of biological variation is required to discriminate these.1 A high degree of individuality results from low intra-individual and high inter-individual variation, leaving popRI as an insensitive method for diagnostic interpretation and clinical decision-making in these situations. To objectively determine the applicability of popRI for haematology interpretation, blood was obtained weekly for five weeks from ten Asian elephants (Elephas maximus) and submitted for manuala and automatedb blood counts. The components of biological variation were established as previously described.1 The degree of individuality was strikingly high for most parameters, indicating that significant changes within an individual may be missed by application of popRI. Anecdotally this is the case for elephant endotheliotropic herpesviruses haemorrhagic disease, where downward trends in platelet counts have been overlooked when interpreted by means of popRI, with fatal consequences. Establishment of critical difference values (the change required in a given parameter required to constitute a significant difference) derived from intra-individual variation, will enable more sensitive interpretation of results from Asian elephants. Importantly, this study underscores that the role of intra-individual variation should be investigated more broadly in zoo species.

aAnimal Health Laboratory, University of Guelph, Guelph, Ontario, Canada.
bAdvia 2120 analyser, Siemens Healthcare Limited, Oakville, Ontario, Canada.

Literature Cited

1.  Fraser CG, Harris, EK. Generation and application of data on biological variation in clinical chemistry. Crit Rev Clin Lab. 1989;27:409–437.


Speaker Information
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Kathryn L. Perrin, BVetMed
Center for Zoo and Wild Animal Health
Copenhagen Zoo
Frederiksberg, Denmark

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