From Frog and Mouse to Dolphin and Elephant: Comparative Hematology and Its Use as a Diagnostic Tool
Nicole I. Stacy, DVM1, DrMedVet, DACVP; Kirstin F. Barnhart2, DVM, PhD, DACVP; Michael M. Fry3, DVM, MS, DACVP
Hematologic evaluation provides valuable information for diagnosis, treatment, monitoring, and prognosis of the individual patient, and for health assessment of animal populations. Differences in mammalian and non-mammalian species extend from basic anatomy and physiology to morphologic and functional features of blood cells.1,2 A major difference is the presence of nucleated erythrocytes and thrombocytes in non-mammalian species. As automated hematology analyzers are programmed to consider all nucleated cells as white blood cells, hematologic analysis of non-mammalian blood relies on manual methods. Accurate interpretation of hemogram results requires knowledge and expertise in sample collection, handling, and analysis, as well as species- (or strain)-specific variations in blood cell morphology and pathophysiologic responses. Understanding of the hematology of non-domestic species is continuously expanding, and laboratory reference intervals are being defined for an increasing number of exotic species.
If population-based reference intervals are not available for a given species, subject-based reference intervals can be helpful in the evaluation during treatment and/or monitoring of the individual patient.³ The objective of this overview is to highlight major differences in morphology, function, and physiologic and pathologic blood cell responses across various taxa of mammalian and non-mammalian vertebrate species, and to summarize important factors that should be considered when interpreting hemogram results.
1. Harvey JW. Veterinary Hematology: A Diagnostic Guide and Color Atlas. 1st ed. St. Louis, MO: Saunders; 2012.
2. Campbell TW, Ellis CK. Avian and Exotic Animal Hematology & Cytology. 3rd ed. Hoboken, NJ: Wiley Blackwell; 2007.
3. Walton RM. Subject-based reference values: biological variation, individuality, and reference change values. Vet Clin Pathol. 2012;41(2):175–181.