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Laboratory evaluation of gastrointestinal disease

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Abstract

The gastrointestinal (GI) tract is relatively inaccessible, and laboratory investigations are an important component of the diagnostic approach to GI diseases. Although alone they often do not provide a definitive diagnosis, they are helpful in ruling out non-GI causes of GI signs, narrowing the list of differential diagnoses and directing further more specialized and potentially more invasive diagnostic procedures. The chapter discusses a diagnostic approach to gastrointestinal problems, routine diagnostic procedures and specialized diagnostic tests. The chapter also contains case examples.

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Figures

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13.1 Overview of investigation of gastrointestinal disorders
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13.8 Assimilation of folate and cobalamin. (a) Dietary folate is present in food as a conjugated form, folate polyglutamate. This conjugate is digested by folate deconjugase, an enzyme on the microvillar membrane, which removes all but one residue. The resultant folate monoglutamate is taken up by specific carriers in the mid small intestine. (b) Following ingestion, cobalamin is released from dietary protein in the stomach. It then binds to non-specific binding proteins (e.g. ‘R-proteins’). In the small intestine, cobalamin transfers on to intrinsic factor (IF), which is synthesized by the stomach (dog) and pancreas (dog and cat). Cobalamin–IF complexes pass along the intestine until the distal small intestine, where cobalamin is transported across the mucosa and into the portal circulation.
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13.13 Faecal parasitology: illustration of comparative egg size of various parasites. (Courtesy of Hoechst–Roussel-AGri Vet Company, USA; permission requested)
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13.14 Faecal parasitology: protozoal parasites. (a) Zinc suphate flotation showing cysts. (b) Stained faecal smear showing characteristic appearance of with its long undulating membrane. (c) cyst (stained). Note the large kidney bean-shaped macronucleus. (d) cyst (not stained). Note that the large kidney bean-shaped macronucleus is not easily observed. (e) Modified Kinyoun’s acid-fast stain of sp. oocysts. spp. are now considered gregarines. (f) Oocysts of spp. in a canine faecal float. Note the two different sizes and that several are sporulated.
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13.15 Faecal parasitology: tapeworms. (a) Proglottids of are often readily apparent in canine faeces. (b) eggs are found in clusters 120–200 μm in size. Individual eggs measure 35–60 μm in diameter and contain an embryo bearing hooks. (c) Taeniid eggs of spp. and spp. are morphologically indistinguishable, measure 25–40 μm, and consist of a thick, striated wall surrounding a hexacanth embryo. (© The National Center for Veterinary Parasitology at Oklahoma State University, www.ncvetp.org/)
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13.16 Faecal parasitology: hookworms. (a) Egg of . Eggs have an elliptical shape, thin shell and are approximately 52–79 × 28 μm. In fresh faeces eggs contain morulae, which develop to first stage larvae within eggs in the environment. (b) Egg of . This hookworm infects dogs (rarely cats) in cooler temperate regions, including the northern USA, Canada and Europe. The eggs resemble those of spp. in that they are elliptical, thin-shelled and contain morulae in fresh faeces, but eggs are slightly larger (71–92 × 35–58 μm). (© The National Center for Veterinary Parasitology at Oklahoma State University, www.ncvetp.org/)
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13.17 Faecal parasitology: ascarids. (a) Egg of . The eggs are 85–90 × 75 μm, subspherical and have a thick and pitted shell. (b) Egg of . The eggs are similar to those of , but are 65 × 75 μm and tend to be more elliptical. (c) Egg of . The eggs are approximately 70–80 μm and resemble those of spp., but have a smooth shell and the embryo takes up less space within the egg. (© The National Center for Veterinary Parasitology at Oklahoma State University, www.ncvetp.org/)
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13.18 Faecal parasitology. (a) Comparative image of (left) and (right) eggs found in a faecal flotation from a dog. Though similar in appearance, is asymmetrical and smaller in size. (b) Faecal flotation showing ova (darker appearing biperculate ova) and ova. (a, © The National Center for Veterinary Parasitology at Oklahoma State University, www.ncvetp.org/; b, Reproduced from the )
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13.19 Faecal parasitology. (a) Larva of . Third-stage larvae are approximately 500 μm and have a tricuspid tail similar to that of the adult female (2nd- and 4th-stage larvae also have this type of tail). Adults and larvae are found in the stomachs of domestic cats and other felids. Diagnosis is based on the identification of larvae or small adults (1 mm) in vomitus using the Baermann test. (b) In fresh faeces, spp. larvae rapidly develop to the infective filariform stage, which enters the host via skin or mucosal penetration. Filariform refers to the elongated shape of the oesophagus. In dogs and cats, eggs frequently hatch before leaving the body, thus free larvae are most often found in fresh faeces. (© The National Center for Veterinary Parasitology at Oklahoma State University, www.ncvetp.org/)
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13.21 SNAP immunochromatographic test for in-house testing for infection.
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13.22 Photomicrograph of a biopsy specimen from the duodenum of an 8-year-old neutered male crossbred dog with diarrhoea, ascites and severe panhypoproteinaemia (albumin 10 g/l, reference interval: 25–31 g/l; globulins 20 g/l, reference interval: 27–40 g/l). There is evidence of villous atrophy, epithelial erosions and mild lacteal dilatation. There is a variable, mixed inflammatory cell infiltrate within the mucosa. These findings are consistent with mixed intestinal inflammation. (Haematoxylin and eosin stain; original magnification X10) (Courtesy of R Fox, University of Liverpool)
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13.23 Cytological specimen (collected by cytology brush) from the duodenum of a 6-year-old neutered male Staffordshire Bull Terrier with chronic vomiting and diarrhoea. The preparation demonstrates clumps of normal epithelial cells. Streaks of nuclear material are due to rupture during smearing. The histopathological specimens from this case were unremarkable and the dog responded to dietary management, suggesting an adverse reaction to food. (Rapid Rapid Romanowsky stain; original magnification X40)
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13.24 Fluorescent hybridization (FISH) in a sample of small intestine from a dog with diarrhoea, fed a raw meat diet. The positions of bacteria are highlighted by the surrounding white boxes. A eubacterial probe shows green fluorescence and appears red.
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13.25 Right lateral abdominal radiograph of the Airedale Terrier with anorexia, vomiting and occasional diarrhoea.
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13.26 Small pedunculated bleeding rectal mass identified during colonoscopy and confirmed histologically as an adenomatous polyp.

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