Equine gastric ulcer syndrome (EGUS) is common in adult horses, but seeking to confirm cases through gastroscopy can be costly and time-consuming. It is also not readily available to most veterinarians.
Researchers set out to examine whether a much simpler sucrose permeability test might represent a simple economical alternative to gastroscopy for screening for stomach ulcers.
While they found that the test wasn’t really successful in detecting EGUS, they suggested that the test might in fact give an accurate representation of the true mucosal integrity of the stomach. They noted that assessments of lesion severity (and even the presence or absence of lesions) using gastroscopy was subjective, and agreement between observers for endoscopic diagnosis was notoriously poor.
Performance horses are particularly susceptible to gastric ulcers, with previous studies showing 47–100% of Thoroughbred racehorses, 44–87% of Standardbred racehorses, 33–93% of endurance horses, and 58–64% of show and sport horses had gastric lesions on gastroscopy.
Non-performance horses are also susceptible, with ulcers found in the gastric mucosa of 11–67% of sedentary horses and horses that partake in less strenuous activities.
So, how could blood sucrose levels provide insights into gastric ulcers? With its large molecular size, sucrose is not able to permeate across the healthy mucous membrane of the gastrointestinal tract. However, it can cross the mucous membrance in the presence of gastrointestinal disease, presumably due to changes in permeability or directly through gaps in the epithelium caused by erosion or ulceration.
If present in blood, sucrose is cleared via the urine; it is not metabolized and the body does not produce it. Therefore, increased amounts of sucrose in the blood after an oral dose of sucrose would point to increased gastric permeability, and could potentially be used to predict the presence of gastric disease.
For the study, researchers Michael Hewetson, Ben Sykes, Gayle Hallowell and Riitta-Mari Tulamo used 101 adult horses with or without naturally occurring gastric ulcers.
They organized an experiment to determine the diagnostic accuracy of blood sucrose as a potential screening test by comparing it to gastroscopy as the gold standard.
All horses enrolled in the study were recruited from those referred to the University of Helsinki Equine Teaching Hospital in Finland for gastroscopy, and from a local riding center.
The horses were used for a wide range of equestrian activities, ranging from dressage to racing.
Horses were excluded if they had received non-steroidal anti-inflammatory drugs or omeprazole within seven days prior to testing.
Owners were asked to withhold food from their horses for 16 hours and water for 6 hours before sucrose testing.
Following the fast, blood samples were collected.
Each horse was then immediately sedated and a gastroscopic examination was performed. The overall prevalence of gastric lesions (ulcers or erosions) was 83%. Fifty eight percent of the horses had gastric lesions that were severe enough to be considered clinically significant – that is, requiring treatment.
Immediately following gastroscopy, the horses were given sucrose at a rate of 1 gram per kilogram of bodyweight, administered via a nasal tube into the stomach as a 10% solution in water.
Blood samples were then taken 45 and 90 minutes after the sucrose for later analysis. A previous study had indicated that peak sucrose concentrations would occur between 45 and 90 minutes after the sugar was given.
The horses were not given food until the final blood sample had been collected.
The researchers found that blood sucrose was neither a sensitive or specific test for detecting equine gastric ulcer syndrome in the mixed group of horses in the study.
“Further studies aimed at evaluating the performance characteristics of the test in different study populations are warranted,” they said.
Given the limitations of endoscopy, due consideration should also be given to alternative methods for comparison of blood sucrose with a gold standard, they said.
Discussing their findings, the authors said it was not immediately evident why the sucrose blood test had a poor diagnostic accuracy in adult horses despite previous literature suggesting otherwise.
“In this study, there was a predominance of glandular lesions (70%) whereas in previous studies, sucrose permeability was assessed primarily on horses with squamous lesions; and it may be that there are fundamental differences in the permeability of the sucrose molecule between the glandular and squamous epithelium.”
Evidence, they said, suggested there were significant differences in the permeation pathway of the glandular versus the squamous epithelium which may explain in part why in this study population, with a predominance of glandular ulcers, the sucrose blood test had a poorer diagnostic accuracy than expected.
However, the sensitivity and specificity of the test for squamous lesions was also poor, albeit less so than for glandular ulcers. That said, very few of the squamous lesions in the study horses were extensive or demonstrated areas of apparent deep ulceration.
“It is therefore possible that in such cases, the total surface area for sucrose permeation was too small to differentiate between affected and unaffected horses.
“Alternatively, the validity of the gold standard itself can be questioned. It may be that the sucrose test is too sensitive and may detect slight and clinically insignificant mucosal damage that cannot be seen on endoscopy, thus limiting its use in clinical decision-making regarding gastric ulceration.
“We postulate that sucrose permeability is in fact an accurate representation of the true mucosal integrity of the stomach based on a number of previous publications documenting its effectiveness in both humans and other species; and that assessment via endoscopy is under- or overestimating the severity or depth of gastric lesions.
“This is based on the fact that assessment of lesion severity (and even the presence or absence of lesions) using gastroscopy is subjective, and agreement between observers for endoscopic diagnosis is notoriously poor, particularly if they are inexperienced.”
They said there was currently little evidence to suggest a direct cause-and-effect relationship between clinical signs of equine gastric ulcer syndrome and the presence, severity or location of gastric ulcers in adult horses. “Therefore, it is possible that the diagnostic accuracy of the sucrose test would be improved when testing a population of horses that were all demonstrating clinical signs at the time of gastroscopy.”
Hewetson and Tulamo are with the University of Helsinki, in Finland; Sykes is with the University of Queensland in Australia; and Hallowell is with the University of Nottingham in England.
Diagnostic accuracy of blood sucrose as a screening test for equine gastric ulcer syndrome (EGUS) in adult horses
Michael Hewetson, Ben William Sykes, Gayle Davina Hallowell and Riitta-Mari Tulamo.
Acta Veterinaria Scandinavica 2017 59:15 DOI: 10.1186/s13028-017-0284-1