"We used to work with another hematology analyzer, and the accuracy was sometimes questioned. Now that we have the LaserCyte®, we always have accurate results. We can count on its accuracy."

Dr. Mauri Karger, Owner
I-20 Animal Medical Center, Arlington, Texas
IDEXX LaserCyte Owner since September 2003

A change in neutrophil numbers can be the first clue that the patient is suffering from a systemic disease

Neutrophils
Dog and cat neutrophils are found in the circulation for only 5.5–7.6 hours, and horse neutrophils circulating, on average, just a little longer. The blood neutrophil count, therefore, represents a single point sampling from a highly dynamic balance between neutrophil production in the marrow and neutrophil migration into tissues. Knowledge of the absolute neutrophil count can help define a specific disease in a patient and aid in arriving at a prognosis.

Neutrophil Function
Neutrophils serve as the primary defense against invasion of tissues by microorganisms. Neutrophils kill bacteria and can also damage or participate in the destruction of mycotic agents, algae and viruses. Neutrophils accumulate at sites of inflammation or bacterial infection by a process of directional migration or chemotaxis.

Cellular and molecular mediators of inflammation generate chemotactic substances, stimulate marrow release, and promote margination and adhesion of neutrophils to vascular endothelium at sites of inflammation. Neutrophils leave the blood stream and enter the tissues by transmigration between endothelial cells. At the site of inflammation, neutrophils are capable of phagocytosis and microbicidal activity. Fusion of lysosomal granules with the phagocytic vesicle releases lytic enzymes and chemicals capable of killing bacteria.

Quality
Changes in the rates of marrow production and release, the exchange between marginal neutrophil pool and circulating neutrophil pool, and/or the rate of tissue migration directly influence the number of neutrophils measured in a CBC. A total white blood cell count and neutrophil count, if given electronically by an impedance-based hematology analyzer, can be falsely increased by large platelets, platelet clumps and nucleated RBCs since impedance counters only look at the size of the cell, some reporting only "medium" or "mid-range" size-cells, not being able to differentiate between neutrophils, eosinophils and basophils.

Neutropenia

• A decrease in the absolute number of neutrophils
• In dogs and cats, neutropenia occurs when the absolute count is less than 3000–4000/µL.
• Neutropenia is the most frequent cause of leukopenia.

Mechanisms of neutropenia include:

• Acute demand or consumption in tissues
• Decreased marrow production
• Ineffective granulopoiesis (dysgranulopoiesis)
• Increased margination from the circulating neutrophil pool to the marginal neutrophil pool

Neutropenia due to acute tissue demand
Neutrophils can rapidly sequester in a well-vascularized tissue hat becomes acutely inflamed or septic (Figure 1).

• Neutropenia results when the rate of migration into tissue exceeds the capacity of the marrow storage pool of neutrophils.
• The inflammatory process is so severe and acute that there is insufficient time for granulopoiesis to replenish the supply of mature neutrophils.
• Bands and some metamyelocytes are released from the marrow, causing a severe left shift.
• Toxic change often will be evident in neutrophils in blood and in precursors in marrow.
• Neutropenia with a severe left shift and toxic neutrophils is seen in conditions such as acute peritonitis, ruptured GI viscus, acute metritis, gangrenous mastitis and acute cellulitis.
• A poor or guarded prognosis is indicated because of the extent and severity of inflammation necessary to produce this neutrophil response.

Neutropenia due to decreased marrow production

• Severe toxic insults to marrow can result in decreased marrow production of neutrophils.
• The bone marrow in these animals is usually hypocellular with a severe reduction in granulocytic, erythroid and megakaryocytic precursors (Figure 2). On occasion, the marrow is very cellular due to extensive replacement by neoplastic cells (myelophthisis).
• Potential causes include: adverse drug reactions, exposure to toxic chemicals and plants, infectious agents, myelophthisis and suspected immune-mediated marrow destruction.
• Drugs that have been incriminated include: estrogen, phenylbutazone, trimethoprim-sulfadiazine, chloramphenicol, griseofulvin and several chemotherapeutic agents.
• Infectious agents include: parvovirus, panleukopenia virus, feline leukemia virus and Ehrlichia.
• Production of RBCs and platelets can also be affected resulting in concurrent nonregenerative anemia and thrombocytopenia.

Neutropenia due to ineffective granulopoiesis

• Neutropenia can occur because of arrested development or a reduction in marrow release in spite of adequate numbers of granulocytic progenitor cells in marrow.
• The bone marrow in these animals is cellular with adequate or increased numbers of granulocytic precursors.
• Diseases associated with this neutrophil response include: myelodysplasia, acute myeloid leukemia, and infections caused by feline leukemia or feline immunodeficiency virus.

Neutropenia due to increased margination

• A sudden shift in neutrophils from the circulating neutrophil pool to the marginal neutrophil pool can cause a transient acute neutropenia.
• Causes include anaphylaxis and endotoxemia
• Neutropenia is an early, transient event and may disappear before the animal is presented for medical treatment.

Neutrophilia
Neutrophilia is an increase in the absolute numbers of circulating neutrophils. In adult dogs and cats, neutrophil counts exceed 12,000–13,000/µL. Neutrophilia is the most frequent cause of leukocytosis.

Causes of neutrophilia include:

• Physiologic or epinephrine-induced
• Corticosteroid- or stress-induced
• Chronic inflammation with marked neutrophilia
• Chronic inflammation with new steady state
• Hemorrhage or hemolysis
• Granulocytic leukemia
• Inherited granulocyte defects

Physiologic neutrophilia

• Epinephrine release causes a transient (1 hour) mature neutrophilia by shifting neutrophils from the marginal neutrophil pool to the circulating neutrophil pool.
• Epinephrine release is caused by fear, excitement, vigorous exercise and seizure activity.
• In cats, a marked lymphocytosis (6,000–20,000/µL) can occur concurrently or be the prevalent finding.

Corticosteroid or stress-induced neutrophilia

• Increased circulating levels of glucocorticoids cause increased release of mature neutrophils into the circulating neutrophils and decreased migration of neutrophils into tissue.
• The response can occur after endogenous secretion or exogenous administration of corticosteroids. Common causes of endogenous release include pain, traumatic injury, boarding, transport or other painful conditions.
• Following exogenous administration, leukocytosis (17,000–35,000/µL) and neutrophilia occur within 4–8 hours and return to normal 1–3 days after treatment.

Neutrophilia of acute inflammation

• Inflammation, sepsis, necrosis or immune-mediated disease cause increased tissue demand and increased marrow release of segmented and band neutrophils.
• Leukocytosis (15,000–30,000/µL) characterized by neutrophilia with left shift and variable monocytosis is the usual response. Toxic neutrophils may be observed.
• Lymphopenia and eosinopenia, reflections of stress and elevated circulating glucocorticoids, are also common.
• Surgical removal or drainage of septic focus may transiently increase the magnitude of the neutrophilia.

Neutrophilia of chronic inflammation

• Some chronic suppurative lesions (e.g., pyometra, abscesses, pyothorax, yoderma) and some neoplasms can cause marrow granulocytic hyperplasia that results in severe leukocytosis (50,000–120,000/µL).
• Laboratory features include neutrophilia with a left shift, variable numbers of toxic neutrophils, monocytosis and often hyperglobulinemia.
• The anemia of inflammation (mild to moderate nonregenerative anemia) is usually present.
• The term "leukemoid response" is used to describe such inflammatory neutrophilias with WBC counts >100,000/µL.

Chronic inflammation with new steady state

• A second form of chronic inflammation is seen where a new steady state has been reached between marrow production and release of granulocytes and tissue demand.
• Total white cell counts are normal or only slightly elevated.
• Neutrophil counts are high normal or only slightly elevated and there is minimal to no left shift.
• Lymphocyte numbers tend to be in the reference range.
• The most consistent leukogram abnormality is monocytosis.
• The anemia of inflammatory disease and hyperglobulinemia are often present.

Hemolytic or hemorrhagic anemias

• Neutrophilias with left shift frequently occur in animals with immune-mediated hemolytic anemia. Leukocytosis can be marked (>50,000/µL).
• Mature neutrophilia occurs three hours following acute hemorrhage.

Chronic granulocytic leukemia

• Usually presents with marked neutrophilic leukocytosis (>80,000/µL).
• Left shift is present and may be disordered with evidence of a maturation arrest. Very young neutrophil precursors (promyelocytes and myeloblasts) may be seen.
• Thrombocytopenia and/or nonregenerative anemia are observed in varying degrees.
• Hepatomegaly and/or splenomegaly may be present due to neoplastic infiltration.
• This condition must be differentiated from the neutrophilia of chronic inflammation.

Inherited neutrophil disorders

• Consider only when other causes can be eliminated.
• B2 integrin deficiency has been recognized in Irish setters and results in decreased neutrophil adhesion to endothelium, diminished chemotaxis and decreased bactericidal activity. These dogs have persistent neutrophilia and recurrent infections.
• Cyclic hematopoiesis or grey colic syndrome is characterized by cyclic fluctuations in neutrophils, monocytes, eosinophils, platelets and reticulocytes at 11–13-day intervals. Neutrophil changes are most pronounced with neutrophilia following 2-to-4-day neutropenic episodes.

Morphology

Normal
Normal circulating neutrophils have the following features (Figures 3 and 4):

• Size—12–15 µ in diameter or 2–2.5 times the diameter of a RBC.
• Nucleus—lobulated or partially segmented with dense, dark purple chromatin.
• Cytoplasm—pale pink or light blue, finely granular, smooth

Most of the circulating neutrophils (95–100%) in normal animals are segmented forms. Very few are band neutrophils. Variation in normal morphology (Figures 5 and 6).

• Prolonged exposure to EDTA prior to preparing the blood film can produce discrete, clear, cytoplasmic vacuoles in the cytoplasm.
• Normal neutrophils have two to four nuclear lobes.
• Five or more lobes indicate hypersegmentation, an aging change, which occurs with prolonged exposure to EDTA, glucocorticoid therapy, hyperadrenocorticism or neutrophilias associated with chronic infections.

In Disease

Toxic neutrophils

• Morphologic changes are apparent in neutrophils of dogs and cats with severe inflammatory disease or toxemia.
• The severity of the morphologic changes is proportional to the intensity of the inflammatory or toxemic disease.
• Morphologic features of toxic neutrophils:
• Diffuse cytoplasmic basophilia—color of the cytoplasm becomes blue-grey.
• Foamy vacuolation of the cytoplasm—irregular clearing in the cytoplasm produces vacuolation.
• Dohle bodies—one or more, irregular, basophilic cytoplasmic inclusions.
• Abnormal nuclear shapes—irregular lobulation or ring-shaped nuclei.
• Toxic change is scored as mild, moderate or severe on a scale of 1+ to 3+.

Infectious agents

• Organisms that can be found in neutrophil cytoplasms include Ehrlichia, Hepatozoon and Histoplasma.
• Canine distemper inclusions are seen occasionally in neutrophil and lymphocyte cytoplasms.

Neutrophil changes with inherited disorders

• Lysosomal Storage Disease—Cats and dogs with mucopolysacharidoses, gangliosidosis have fine, purple cytoplasmic granules in neutrophils.
• Chediak-Higashi Syndrome—small, round pink granules are present in neutrophil cytoplasm.
• Pelger Huet Anomaly
• Occasionally seen in dogs
• Neutrophil and eosinophil nuclei are hyposegmented, but have dark, condensed mature chromatin patterns.
• Neutrophils and eosinophils are functionally normal so the condition is not clinically significant.
• Must be differentiated from a true left shift
• Also occurs in rabbits where the anomaly occurs in association with other fatal heritable abnormalities

The recommendations contained in Diagnostic Edge educational materials are intended to provide general guidance only. As with any diagnosis or treatment, you should use clinical discretion with each patient based on a complete evaluation of the patient, including physical presentation and complete laboratory data. With respect to any drug therapy or monitoring program, you should refer to product inserts for a complete description of dosages, indications, interactions and cautions.

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LaserCyte® software upgrade (version 1.17)

Is your LaserCyte Hematology Analyzer operating on the latest software version 1.17?

Software version 1.17 includes enhancements to the analysis algorithms, user interface and operational sequences, including the following two major new features and functions:

• Automatic performance of daily vent tube maintenance

• The ability to perform a complete in-house CBC for equine patients

To ensure that you are operating with this software version, simply tap the Instruments button on the main screen of your LaserCyte Hematology Analyzer, and then tap the System tab. The software version that you are using on will be displayed as illustrated in the figure below.

If you are not currently operating on 1.17 and have received your software upgrade, please upgrade immediately by following the three-step procedure outlined in the 1.17 software upgrade packet.

If you are not currently operating on 1.17 and have not yet received your software upgrade, please contact the IDEXX LaserCyte Support Team at 1-800-248-2483.

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Dover, Delaware
Wednesday, April 14
Delaware VMA Spring Meeting
Modern Maturity Center

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Running three different patients and species simultaneously with IDEXX VetLab®

Did you know you could run multiple patients on your various IDEXX VetLab equipment at the same time?

If you want to run one patient's CBC on your LaserCyte and another patient's chemistry profile on your VetTest analyzer, simply enter the first patient's information and choose the analyzer you want to use. After initiating that test, the touchscreen will return to its home screen. Tap the Sample button again and enter in your next patient's information. On the next screen, choose the instrument you want to use. Note that the instrument that is processing your first sample is grayed out and cannot be selected. Proceed as usual.

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... and we want you to hear from us! Pass the following link along to your friends and colleagues. They can register for the Diagnostic Edge to learn more about hematology, stay informed of the latest IDEXX hematology products and services, and respond to various customer and market surveys that we will soon offer. Registration is easy at www.idexx.com/diagnosticedge.

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