Causes of erroneous white blood cell counts and differentials in clinically healthy young northern elephant seals (Mirounga angustirostris)

From 1993 to 1995, approximately 10% of the clinically healthy northern elephant seals (Mirounga angustirostris) at The Marine Mammal Center in California exhibited a large unexplained increase in their white blood cell (WBC) count. In these animals, WBC counts ranged from 28,780 to 125,000/mm³, with a mean of 50,087/mm³. Significant correlations between the leukocytosis and weight gain and day of admittance were identified, but no correlation existed between leukocytosis and general state of health, sex, length of stay, or diet. Bone marrow contamination of blood samples, erroneous automated leukocyte counts, and leukogram changes consistent with subclinical inflammation were the major factors contributing to the elevated WBC counts in these apparently clinically healthy animals.