Lymphocytosis is a blood disorder of cats defined as an absolute number of circulating lymphocytes greater than reference range of 7 x 109/L or >7000/µl, and below 15,000/µl (the reference cut-off for a diagnosis if leukemia).
Absolute lymphocyte counts are greater in kittens than adults. Young kittens - absolute lymphocyte count increases from birth to a maximum at approximately 12-14 weeks of age of 10.5 x 109/l; value is within reference range for adults by 16-20 weeks of age.
- - Physiological lymphocytosis due to stress - absolute lymphocyte count can rise to >10,000/µl and is much greater than the relatively mild increase in mature neutrophils that accompanies this type of lymphocytosis.
- - Neoplasia - with lymphosarcoma or lymphocytic Leukemia, peripheral blood lymphocyte count can range from lymphopenia to counts >100,000 lymphocytes/µl. Significantly high counts (i.e., > 30,000/µl) are uncommon.
- - Antigenic stimulation due to
- - Hypoadrenocorticism - lymphocytosis is accompanied by mild eosinophilia and the absence of neutrophilia or monocytosis in a sick and stressed animal.
- - Hyperthyroidism - approximately 10% of cats with hyperthyroidism have lymphocytosis.
- - Methimazole is associated with lymphocytosis in 7% of cats treated for hyperthyroidism.
Treatment must be directed at the primary disease causing lymphocytosis.