AJP - Regulatory, Integrative and Comparative Physiology, Vol 256, Issue 6 1220-R1224, Copyright © 1989 by American Physiological Society
Influence of hematocrit on whole blood glucose levels: new evidence from marine mammals
M. A. Castellini and J. M. Castellini
Long Marine Laboratory, University of California, Santa Cruz 95064.
The water content and glucose concentration in the whole blood of marine
mammals were found to be correlated to red blood cell concentration.
Because hematocrit (Hct) undergoes significant periodic shifts in these
mammals during periods of apnea and/or diving, the measured values of whole
blood glucose change due to alterations in Hct, independent of shifts in
metabolite regulatory pathways. In contrast to humans, where red blood cell
and plasma glucose concentrations are equivalent, in most other mammalian
species red blood cell glucose concentration is much lower than that in
plasma. Therefore, as Hct increases, the whole blood concentration of
glucose must decrease in a linear manner, depending on the magnitude of the
Hct change and the concentration of glucose in the blood cells. This study
demonstrates that water and metabolite distribution must be considered when
interpreting whole blood metabolite data. The results suggest that plasma
or serum analysis of metabolites would avoid distribution problems. This is
especially critical in species where Hct varies during the course of the
experiment, as in exercising or diving mammals.
