October 6, 2015

???The Need For a Reliable Diagnostic Test for GI Tract Disorders

emma-hardyBy Dr. Emma Hardy.

Extensive research conducted by Freedom Health LLC, and independently at the University of Glasgow School of Veterinary Medicine, is shifting the spotlight in equine gastrointestinal (GI) disease towards the hindgut, and specifically disorders of the mucosal lining. Still, these disorders remain largely under-reported. Indeed, the number of published articles relating to gastric ulcer syndrome over the past year number in the region of 900, whilst those published in reference to colonic inflammation and/or ulceration number just nine.

This under diagnosis is due in part to limitations on current diagnostic techniques (Pellegrini, 2005):

  • Gastroscopy, a now commonplace procedure, allows for visualisation of the stomach and proximal duodenum only, leaving the remaining 70 feet of small intestine plus the caecum and colon unobserved.
  • Colonoscopy beyond the distal portion of the colon would carry with it a high risk of mortality, due to its highly invasive nature and the evacuation of the bowel required for this procedure (Kerbyson et al. 2014)
  • Abdominal ultrasonography is routine in the diagnosis of colitis, where thickening of the colon wall and submucosal oedema is highly characteristic. However, this remains an in-patient procedure, and the interpretation of the image is very dependent on the experience and skill of the operator (Glavin et al. 2004)
  • Rectal biopsy, a particularly invasive procedure, has been found to be useful in the diagnosis of intestinal disorders (Lindberg et al. 1996) but, whether a biopsy might histologically reflect the mucosa/submucosa of the more cranial intestinal tract is questionable (Peek, 2010).

SFBTcasfinal 2011_ccColonic ulceration and inflammation can elicit a range of symptoms, from hindgut discomfort and recurrent colic to loss of performance and condition and even, behavioural and lameness issues (Pers Comms). Often these symptoms, which are frequently vague and non-specific, are attributed to alternative causes. As a result, by the time consideration is given to a disorder of the GI tract, and specifically of the hindgut, the health of the horse may be at a critical stage with limited treatment options, carrying greater risk to the animal and cost for the owner. By understanding a disease process at an earlier point, and having a reliable method to aid diagnosis, proactive steps can be taken to correct it. This gives rise to the importance of reliable diagnostic methods for gastrointestinal disease.

A Faecal Test Provides an Initial Screening

The SUCCEED Equine Fecal Blood Test is a diagnostic aid which, in conjunction with the veterinarian’s expertise and other diagnostic measures, helps to achieve a diagnosis for GI tract disorders. The completely non-invasive stable-side test detects occult equine albumin and haemoglobin in a faecal sample. These marker proteins serve as indicators of gastrointestinal conditions, wherein their presence in a faecal sample indicates the presence of inflammation and/or blood loss.

Because of differences in the nature of albumin and heme, the presence or lack of these proteins serves to indi- cate where in the equine GI tract they originate. Albumin, but not heme, is naturally degraded by acids and proteinases (Carter & Pellegrini, unpublished) which are introduced into the small intestine via the common bile duct at a point just past the stomach. As a result, detection of albumin in a faecal sample serves as a proxy for inflammation in the hindgut. When the two markers are evaluated together they can enable conditions to be pinpointed as foregut, hindgut, or both Table 1.

table1-fbt-results

The FBT is highly sensitive but non-specific. Akin to a thermometer, it is intended to be an indicator of disease rather than confirming a specific disorder. It has been developed to initiate the process of diagnosis, which in turn, helps the clinician to select the most appropriate and effective additional investigations and best treatment options for optimal recovery.

How is the FBT used?

The FBT is entirely self-contained, requires no laboratory analysis or additional processing and, has been designed to be easily used at the point of care. This also negates the need for a horse to be transported to a clinic for testing, or even for a vet to attend should a fresh faecal sample be provided to the practice for immediate testing. The FBT takes the form of a two-part test cassette, packed inside a plastic screw top bottle (used for sample collection) along with a pipette, vinyl glove and set of instructions. The cassette contains two wells, and two wicking/ viewing windows, one each for detection of albumin and haemoglobin. Two drops of the faecal sample and water solution is placed into each well, and the results appear within 15 minutes.

The FBT detects blood components from any source. While the presence of blood proteins in a faecal sample likely derive from the GI tract, care should be taken to ensure the FBT is not run in situations where blood may be introduced into either the GI tract or the faeces from external sources.

using-succeed-fbt

Development and Validation

Faecal blood testing originated from human medicine, where guaiac stain was used to detect the pseudoperoxidase activity of the heme portion of haemoglobin, and initial studies investigating the incidence of colonic ulceration in horses employed this method. This technique however lacked sensitivity and some question existed over the possibility of false positives resulting from chlorophyll in the equine diet mimicking peroxidase molecules (Sinatra et al. 1999). The FBT overcomes these limitations by using an immunoassay (ELISA) with highly specific antibodies raised against equine heme and equine albumin.

Several hundred post-mortem examinations were conducted in the process of correlating FBT findings
to actual pathology of the gastrointestinal mucosa. The protocol involved collecting and testing faecal balls using the FBT and then correlating the results with independent visual observations of the stomachs and large colons of the subject horses. The statistical reliability of the test was calculated based on the results of the most recent necropsy study in October 2011 with 178 horse subjects Table 2.

table2-ppv-npv-fbt

These data illustrate the highly sensitive, minimally specific nature of the test. Only 11 horses of the 178 inves- tigated did not show some kind of ulcerative, proliferative or haemorrhagic lesion in either the stomach or colon. This low number of true negatives influenced the calculation of the NPV number.

The importance of the FBT as a diagnostic aid is not limited to GI tract ulceration. It can be used to facilitate diagnosis of numerous GI tract disorders, characterised by a loss of protein or whole blood, and to monitor recovery, and even efficacy of treatment options. The FBT is routinely used to help provide more information in horses with suspected colitis, IBD, colic, unexplained loss of weight/condition/performance, changes in temperament, and protein losing enteropathy. The scope of the FBT is also not limited to only faecal testing. In the event of a hypoalbuminaemia, simple FBT testing of both faecal and urinary samples can help identify the presence of an enteropathy or nephropathy.

Due to its supporting role in diagnosis of disease, the SUCCEED Equine Fecal Blood Test is available only to veterinarians.


This article is was included in a full piece on
“Digestive health and the modern horse
inserted as a supplement in the May/June 2015 issue of Equine Health.
Click to view and download a PDF of the complete supplement:
GI-Health-Modern-Horse

References

Galvin N, Dillon H, McGovern F (2004) Right dorsal colitis in the horse: mini review and reports on three cases in Ireland. Irish Veterinary Journal 57 (8): 467-73

Kerbyson N, Parkin TDH, Knottenbelt DC (2014) The effect of parasite burden on faecally excreted albumin. American College of Veterinary Internal Medicine Forum, Tennessee, USA

Lindberg R, Nygren A, Persson SGB (1996) Rectal biopsy diagnosis in horses with clinical signs of intestinal disorders: a retrospective study of 116 cases. Equine Veterinary Journal. 28(4): 275-284

Peek SF; (2010) ‘How to’ perform a liver, kidney and rectal biopsy. British Equine Veterinary Association Congress, Birmingham, UK

Pellegrini F (2005) Results of a large-scale necroscopic study of equine colonic ulcers. Journal of Equine Veterinary Science. 25(3): 113–117

Pellegrini F, Carter S The Use of Novel Antibody Tools to Detect the Presence of Blood in Equine Feces. Unpublished

Sinatra MA, St John JB, Young GP (1999) Interference of plant peroxidases with guaiac based faecal occult blood tests is avoidable. Clinical Chemistry 45:123–126

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