Clinical pathology in practice

image of Clinical pathology in practice
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Over recent years there has been an increase in the recognition of the value of clinical pathology to veterinary practice. Most cases that require more than superficial first aid will now undergo some laboratory evaluation. This approach to case management encourages therapeutic intervention that is both prompt and appropriate for the animal, and usually improves the outcome of cases. This in turn provides an increase in satisfaction for both the clients and the practice team. This chapter provides an introduction to the key features of laboratory practice. It comprises three distinct sections. Firstly it considers when and how to use an external commercial laboratory and also what features to look for when choosing a laboratory. Secondly, it reviews how to successfully set up a laboratory in the clinic and how to go about managing it for best practice. Finally, it focuses on the key laboratory techniques of microscopy, notably urinalysism haematology and cytology. Cumulatively these sections provide a background to the essential concepts within clinical pathology, a practical guide to laboratory management and an overview of the essentials of microscopy.

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12.2 Blood films (Wright’s stain; original magnification X1000). Film made from fresh ethylene diamine tetra-acetic acid (EDTA) blood showing four morphologically normal leucocytes. Clockwise (from top left): neutrophil; eosinophil; macrophage; and lymphocyte. Film following 5 days of storage at room temperature in EDTA. The erythrocytes have spiky projections and are known as echinocytes or burr cells. Poorly preserved leucocytes are seen also. Clockwise (from top left): eosinophil with pyknotic nucleus; a lysed unidentifiable cell; a neutrophil with vacuolation of the cytoplasm; and a probable lymphocyte with a pyknotic and karyorrhectic nucleus.
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12.5 An example of a risk assessment form.
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12.12 An example of equipment log form.
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12.15 Principles of the quality assurance cycle with reference to laboratory practice.
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12.26 Normal erythrocytes, some of which are polychromatic (pale blue hue) (Wright’s stain; original magnification X1000).
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12.27 Alterations in erythrocyte colour and size. Spherocytes (arrowed) (Wright’s stain; original magnification X1000). Microcytic, hypochromic erythrocytes. Normal erythrocytes (arrowed) and a schistocyte (*) are also visible (Wright’s stain; original magnification X1000).
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12.28 Alterations in erythrocyte shape. Crenation of the erythrocytes. A pyknotic neutrophil is also present (Wright’s stain; original magnification X1000). Acanthocytes (arrowed) (Wright’s stain; original magnification X1000). Target cells (a type of leptocyte) (Wright’s stain; original magnification X2000).
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12.29 Internal erythrocyte structures. Nucleated erythrocyte (Wright’s stain; original magnification X1500). Erythrocytes containing Howell–Jolly bodies (Wright’s stain; original magnification X1000). Heinz bodies (arrowed) are present within most erythrocytes. They appear as pale grey blebs within the erythrocytes or on the erythrocyte membrane (Wright’s stain; original magnification X1000).
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12.31 Leucocytes (clockwise from top left): neutrophil; eosinophil; monocyte; and lymphocyte (Wright’s stain; original magnification X1500). Large toxic immature neutrophil (band) showing Döhle bodies in the cytoplasm (Wright’s stain; original magnification X1500).
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12.32 Platelet clumps (arrowheads). Note also the rouleaux (arrowed) and echinocyte (*) (Wright’s stain; original magnification X1000).
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12.34 Aggregate (arrowheads) and punctate (arrowed) reticulocytes visible in a blood sample from a cat (new methylene blue stain; original magnification X1500).
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12.35 Differences between rouleaux and agglutination. Erythrocytes showing rouleaux (Wright’s stain; original magnification X1000). Erythrocytes showing microscopic agglutination (Wright’s stain; original magnification X1500).
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12.38 The basic cellular structures used in cytological descriptions.
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12.39 Description and interpretation of inflammatory cells. Well preserved neutrophils (Wright’s stain; original magnification X1000). Degenerating neutrophils (Wright’s stain; original magnification X1000). Active macrophages. Note the size of the neutrophil for comparison (Wright’s stain; original magnification X1000). Numerous eosinophils with numerous pink staining cytoplasmic granules (Wright’s stain; original magnification X1500).
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12.40 Description and possible interpretation of non-inflammatory cells. Numerous mast cells accompanied by some eosinophils (Wright’s stain; original magnification X1500). Classic histiocyte round cells from a histiocytoma (Wright’s stain; original magnification X500). Epithelial cells. Note the clump of benign prostatic cells from a prostatic aspirate (Wright’s stain; original magnification X500). Mesenchymal cells (Wright’s stain; original magnification X700).
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12.41 The criteria for malignancy. Anisocytosis and anisokaryosis. Note the two cells of same origin with varying nuclear and cytoplasmic sizes (Wright’s stain; original magnification X700). Clumped, coarse chromatin and marked pleomorphism (Wright’s stain; original magnification X700). Multinucleation (Wright’s stain; original magnification X700).
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