Hemograms consist of both quantitative data (total cell counts, differential cell counts, red cell indices, etc.) and qualitative data (blood film morphology). Proper interpretation depends on the integration of both.
Proper interpretation also depends upon the development of a systematic approach for both quantitative and qualitative data; we recommend evaluation of white cells first, followed by red cells, and then platelets.
For all cell compartments, interpretation can be guided by asking and answering a series of well-designed questions.
WHITE CELLS (Table 1)
› Quantitative data includes total white cell count and differential count
› Qualitative data is white cell morphology
› Key questions include:
- Is there evidence of inflammation?
- Is there evidence of stress?
- Is there evidence of tissue necrosis?
- Is there evidence of systemic hypersensitivity?
- If inflammatory, can the response be classified as acute, chronic, or overwhelming?
- Is there evidence of systemic toxemia?
Is there evidence of inflammation?
› Persistent eosinophilia, monocytosis, and a neutrophilic left shift (increased numbers of immature neutrophils), alone or in combination, suggest inflammation.
› Total white cell count merely reflects balance between marrow production and tissue utilization; in inflammation, total white cell counts may be low, normal, or high.
› Absolute neutrophilias of greater than 25,000/µl are also suggestive of inflammation.
Is there evidence of stress (high circulating levels of glucocorticords)?
› Stress typically results in mild lymphopenia (lymphocyte counts between 750/µl and 1500/µl).
› Eosinopenia, mild neutrophilia, and mild monocytosis may also be present but are less consistent and nonspecific.
Is there evidence of tissue necrosis?
› Monocytosis indicates tissue necrosis and demand for phagocytosis. Monocytosis can occur with acute or chronic inflammation or necrosis.
Is there evidence of systemic hypersensitivity?
› Persistent eosinophilia and/or basophilia is an indicator of systemic hypersensitivity.
› Causes include:
- Parasitic diseases with a systemic component, eg., heartworms, flea bite dermatitis
- Allergic tracheobronchitis in dogs (pulmonary infiltrates with eosinophils)
- Feline asthma
- Allergic gastroenteritis
- Systemic mastocytosis
- Disseminated eosinophilic granuloma complex in cats
- Parasitic disease confined to the intestinal tract (eg., whip worms) does not cause eosinophilia!!
Can the inflammatory response be classified as acute, chronic, or overwhelming?
› In many cases, inflammatory leukograms cannot be further classified.
› In other cases, the differential cell count is typical of acute, chronic, or overwhelming inflammation.
› These typical patterns reflect changes in leukocyte kinetics, or the balance between white cell production in the marrow and white cell utilization in the tissues. These changes are controlled by chemotactic factors and cytokines.
› The typical acute inflammatory leukogram is characterized by neutrophilia with increased band cells (a regenerative left shift), lymphopenia, and variable monocytosis.
- Neutrophilia reflects a large bone marrow storage pool in dogs and cats and the movement of larger numbers of neutrophils from marrow into blood than are moving from blood into tissues.
- The left shift suggests depletion of the marrow storage pool of neutrophils with the subsequent recruitment of younger cells into circulation.
- The lymphopenia reflects stress, a common accompaniment of acute inflammatory processes.
- When present, the monocytosis reflects demand for phagocytosis/tissue necrosis.
› There are two patterns typical of chronic inflammation:
- Marked leukocytosis (50,000-120,000/µl) with marked neutrophilia and left shift, neutrophil toxicity, and monocytosis.
› Most commonly seen with severe focal suppurative lesions
› Usually accompanied by the anemia of inflammatory disease and hyperglobulinemia
› Normal to slightly elevated white cell count characterized by normal to slightly elevated neutrophil counts, no left shift, normal lymphocyte counts, and monocytosis.
› The normal to slightly elevated neutrophil count reflects a new balance between marrow production and tissue demand. This balance results from expanded production of neutrophils by the bone marrow in response to cytokines (growth factors) released at the tissue site of injury.
› The lack of left shift reflects the fact that marrow production of neutrophils has expanded to meet increased tissue demand.
› The normal lymphocyte count reflects the counterbalancing effects of stress and antigenic stimulation on lymphocyte numbers.
› Monocytosis reflects demand for phagocytosis/tissue necrosis.
› The typical overwhelming inflammatory response is characterized by reduced neutrophil numbers, a left shift, lymphopenia, and variable monocytosis.
- Reduced numbers of neutrophils suggest inability of marrow production to keep pace with tissue demand.
- Left shift indicates depletion of marrow neutrophil storage pools.
- Lymphopenia reflects stress.
- When present, monocytosis indicates tissue necrosis/demand for phagocytosis.