UNDERSTANDING AND INTERPRETING HEMATOCRIT MEASUREMENTS IN PINNIPEDS

Hematocrit data are relatively easily obtained from blood samples of p innipeds but differences in methodology and variable physiological con ditions of the subjects can significantly alter their values. This two -fold problem makes comparative data and modeling efforts difficult. T o quantify the difficulty of obtaining accurate and representative hem atocrit values in pinnipeds, hematocrit was measured by both microcent rifugation and Coulter counter methods in a range of pinnipeds under a variety of physiological and handling conditions. The data show that the Coulter counter hematocrit values were 4%-15% higher than those me asured by microcentrifugation. In addition, blood samples from restrai ned animals showed consistently elevated hematocrit values relative to testing subjects. A significant difference was also found between hem atocrit values from pups and adults. Finally, hematocrit was shown to decline over the course of isofluorane anesthesia. Taken together, the se results suggest that labotatory methodology, developmental state, a nd animal handling techniques can significantly alter hematocrit value s in pinnipeds. Thus, modeling efforts that require representative hem atocrit values, such as calculations of total blood oxygen stores, can be markedly impacted by variations in hematocrit measurement techniqu es and sampling regimes.