“Unfortunately, in the population of adult horses that we studied, the test appears to be a fail in that it’s not sensitive enough to reliably identify horses with EGUS,” said Michael Hewetson, BSc (Hons), BVSc, Dipl. ECEIM, an internal medicine specialist at the University of Helsinki Faculty of Veterinary Medicine, in Finland.
“It’s a disappointment, as we were hopeful that the diagnostic accuracy of the test would be good following some promising early results in a pilot study that we had performed back in 2006,” he said.
That 2006 study, which focused on sucrose content in blood samples, followed a 2004 pilot study on sucrose levels in urine.
In their most recent study, Hewetson and his fellow researchers examined 101 leisure and competition horses for the presence of EGUS using two methods: the experimental sucrose permeability test and a gastroscopy.
Gastroscopy—viewing the horse’s stomach through a tube passed through his nostril—is the “gold standard” for diagnosing EGUS. But gastroscopies are both expensive and complex, Hewetson said.
The team’s experimental sucrose permeability test is based on the fact that sucrose molecules are large and don’t penetrate a healthy stomach wall easily. “Sucrose usually passes through the stomach and into the small intestine, where it is rapidly broken down into fructose and glucose, which are then absorbed as an energy source,” Hewetson said.
But that’s only the case for healthy stomachs, he noted. Ulcers damage the stomach wall, making it more permeable to larger molecules like sucrose. So, theoretically, sucrose molecules would be taken up into the bloodstream shortly after the horse ingests them, suggesting the presence of ulcers.
Unfortunately, theory did not line up with reality in Hewetson’s study. “Sensitivity was only 79% for the glucose test, and for a screening test to be valuable, it should have a sensitivity of at least 90%,” he said.
Hewetson said it’s possible the results could indicate that gastroscopy isn’t 100% accurate, either. “Assessments via gastroscopy might under- or overestimate the severity or depth of gastric lesions,” he said. “The 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. Furthermore, it has been demonstrated that there is low correlation between endoscopic assessment of gastric ulcers and histological appearance at necropsy.”
It’s also possible that the sucrose test is simply too sensitive, picking up damage to the stomach walls that aren’t necessarily—or aren’t yet—ulcers, he said.
His study could also have been influenced by a high rate of glandular ulcers, Hewetson added. Glandular ulcers occur in the bottom two-thirds of the horse stomach, which is lined with thick, bumpy glands that produce digestive acids and have a dense layer of mucus and bicarbonate (a pH buffer, also found in baking soda) that protects the wall from stomach acid. That’s opposed to the top third of the stomach that’s nonglandular and lacks protective qualities.
While most EGUS lesions usually occur in the nonglandular section, 70% of the lesions Hewetson identified in his study occurred in the glandular region. Additionally, 83% of the horses had ulcers—an increase of 30% compared to other averages.
“Glandular lesions may have been underreported in previous studies, and I believe they are more prevalent than many people assume,” he said. “Interestingly, it appears to be a disease that is highly prevalent in nonracehorses, and recent work that I have published into the cause of glandular ulcers suggests that this may be related to stressors such as multiple handlers and riders.”
Despite the initial disappointment, Hewetson said his team will continue their research in hopes of finding a way to make the test work. “It’s not all doom and gloom,” he said. “The use of sucrose as a marker of gastric injury is well-established in human medical literature, and there is no reason why it should not work in horses. We just need to think how we can modify the test to improve its sensitivity. I do not think we should give up just yet.”
The study, “Diagnostic accuracy of blood sucrose as a screening test for equine gastric ulcer syndrome (EGUS) in adult horses,” was published in Acta Veterinaria Scandinavica.