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are then evaluated more closely using the 100X, oil immersion lens.
Left shift – the presence of excessive numbers of immature neutrophils (> 300 bands / Fl of blood) in the peripheral blood. Most of these cells are band neutrophils with
fewer metamyelocytes (Figures on right), myelocytes
and progranulocytes (promyelocytes) in decreasing
order of frequency. When the most immature forms (metamyleocyetes and myelocytes) are relatively few compared to the band neutrophil population, the left shift
is said to be pyramidal and complete. This is a favorable response. The extent of the left shift (how immature the cells are) will indicate the severity of the disease. The magnitude of the response (numbers of immature cells) will indicate the ability of the bone marrow to respond to the disease.
Regenerative left shift – a left shift in which there is typically a neutrophilia and there are a higher numbers of mature cells than immature. This is a favorable response where the bone marrow has had suf cient time (3 –5 days) to respond to peripheral demands for neutrophils.
Degenerative left shift – a left shift in which there are more immature neutrophils (bands, metamyelocytes and myelocytes) than mature neutrophils (segmented). Total neutrophils counts are typically low or only slightly elevated. This indicates that the reserve of mature neutrophils in the bone marrow has been depleted, has had insuf cient time to respond, or cannot meet the overwhelming demand for neutrophils. In most species this is an unfavorable prognostic indicator.
Toxic Change - One important change in neutrophils
is the presence of cytoplasmic toxicity. It is particularly important to evaluate toxicity of neutrophils in patients with a leukocytosis, leukopenia or a left-shift. Toxicity
is a cytoplasmic change which is usually associated
with the presence of bacterial infections or toxins. It results from a maturation arrest in cell development,
and therefore occurs in bone marrow precursor cells. Toxicity is semi-quantitated in order of increasing severity from +1 to +4. A +1 Toxicity is de ned by the presence of Döhle bodies; small, basophilic aggregates of RNA
in cytoplasm of cells. This may be normal if seen in low numbers of neutrophils in cats. A +2 Toxicity is de ned as Döhle bodies and diffuse cytoplasmic basophilia. A +3 Toxicity would contain all of the above plus foamy cytoplasmic vacuolation, and a +4 Toxicity would have all of the above plus giantism and/or nuclear lysis.
Reactive Change
Lymphocytes do not develop toxicity, but may become reactive as a result of some antigenic stimulation from an infectious agent, neoplasm, or immune-mediated disease. The cytoplasm of reactive lymphocytes becomes more intensely basophilic, almost a royal blue. Reactive monocytes may also be seen if the cytoplasm becomes more intensely basophilic and
An Urban Experience
vacuolated. This usually indicates a chronic in ammatory process or may be seen with hemoplasmas in the cat.
Neoplastic Cells in Circulation
Neoplastic cells, primarily those of hematopoietic origin, can also be identi ed in the peripheral blood. These cells would alert the clinician to the possibility of leukemia, however, in many cases this diagnosis is con rmed by evaluating the bone marrow. Hematopoietic blast cells may be of erythroid, granulocyte, monocyte, or rarely megakaryocyte origin (myeloproliferative disease), or lymphoid origin (lymphoproliferative disease). In general, blast cells are identi ed as large cells with nuclei often
2 or more times the size of erythrocytes. They often
have abnormal nuclear morphology including high N:C ratio, diffuse, altered chromatin pattern, and prominent nucleoli. The cytoplasm of these cells is often deeply basophilic. The presence of blast cells in the peripheral circulation would alert the clinician to the possibility of an acute leukemia, whereas the presence of unexplained elevations in mature leukocytes (neutrophils, lymphocytes, monocytes, eosinophils, or basophils) would suggest
the possibility of a chronic leukemia. In addition to being classi ed as acute or chronic depending on the maturity of the neoplastic cell, leukemias are also classi ed as a myeloproliferative (erythroid, myelogenous, or monocytic leukemia) or a lymphoproliferative (lymphoid leukemia) depending on the cell line from which the neoplastic population arises. Since leukemia is de ned as a bone marrow neoplasm of the hematopoietic cells, a bone marrow evaluation is often required to make a de nitive diagnosis. A list of the various types of acute and chronic leukemias is provided. In general, chronic leukemias
have a better long-term prognosis than acute leukemias and lymphoid leukemias have a better prognosis than myeloproliferative disorders.
Lymphoid Leukemias Chronic Lymphoid Leukemia
Acute Lymphoblastic Leukemia (ALL) Chronic Lymphocytic Leukemia (CLL)
Acute Myeloid Leukemias Chronic Myeloid Leukemias
Acute myelogenous leukemia (AML) Chronic myelogenous leukemia (CML)
Erythroid leukemia Eosinophilic leukemia
Acute myelomonocytic leukemia Basophilic leukemia
Acute monocytic leukemia Polycythemia vera
Megakaryoblastic leukemia
Acute Myelogenous leukemia Acute Lymphocytic Leukemia Chronic Lymphocytic Leukemia
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