New method may improve blood test’s ability to detect inflammation in horses

Inflammation can help the body when injured or sick by delivering immune cells, promoting healing and more. Chronic or excessive inflammation, however, can cause further damage and lead to additional disease or injury. Clinicians often rely on patient history and current complaints, along with physical examination and blood tests, to determine if inflammation is acute or chronic—but that becomes complicated when the patient is a horse.

Why early detection matters in horses

Early detection of inflammation in horses is crucial to allow for timely treatment, which can prevent chronic issues, reduce pain, and improve the animals’ overall well-being and performance. A test called a complete blood count (CBC), which is also used in humans to quantify blood cells and measure their characteristics, is routinely used by veterinarians to assess health status, but current reference intervals used in CBCs are not designed to specifically detect inflammation.

To enhance the ability to identify inflammation in horses using CBCs, a team of animal scientists at Penn State developed inflammatory indices—mathematical combinations of complete blood count values—that serve as biomarkers that more accurately reflect inflammation indicators in CBC results. These indices integrate information from different white blood cell subtypes and platelets to provide a composite picture of the body’s inflammatory status.

The study is published in the Journal of Equine Veterinary Science.

Limitations of current CBC reference ranges

“A horse could have mild inflammation and still have ‘normal’ complete blood count values because the reference intervals—in other words, the normal CBC ranges—were created using horses that appeared healthy, even though some might have had early inflammation,” said study first author Molly Friend, a doctoral candidate in the Intercollege Graduate Degree Program in Integrative and Biomedical Physiology.

“These industry standard reference intervals are not designed specifically to detect inflammation, so they can miss subtle inflammatory changes.”

Friend is advised by Danielle Smarsh, associate professor of equine science in the Department of Animal Science in the College of Agricultural Sciences and senior author on the study.

How new inflammatory indices were developed

Instead of only looking at single CBC values for specific blood cells, the researchers focused on ratios and indices between different types of white blood cells, which can reveal the balance between the innate (rapid, general) and adaptive (slower, specific) immune responses.

The researchers collaborated with veterinarians in Centre County and several Pennsylvania horse farms, testing nearly 200 horses—some healthy, some sick. The researchers looked at two acute phase proteins captured in CBCs called serum amyloid A and haptoglobin—special proteins that rise in the blood during inflammation—alongside other CBC results.

Based on those results, they were able to assign 48 horses to a group called “inflamed” and 150 horses to a group labeled “not inflamed.” From the second group, the team calculated normal blood value ranges, and then they compared the complete blood count and results from the inflammation index they created for the inflamed group.

Potential impact for veterinarians and horses

“The new non-inflamed reference intervals—based on only healthy horses—were slightly better at detecting inflammation than the broader industry standard reference ranges, but what was most exciting was how the inflammatory indices performed,” Friend said. “These results suggest that using inflammatory indices and reference intervals based on non-inflamed horses can help veterinarians detect inflammation earlier and more accurately in horses. This study is a step toward using routine CBCs to spot inflammation before it becomes serious.”

Because inflammation in horses is so complex, the more tools that researchers can give to veterinarians, the better context they can have around diagnosing an inflammatory response, explained Smarsh.

“We were able to take a pretty large population of horses and analyze the acute phase proteins so we could tell whether or not they were inflamed, and then used this data to calculate the inflammatory indices,” she said. “This has not been done before in horses, and opens up possibilities for veterinarians to have another diagnostic tool at their disposal.”

Contributing to the research were Burt Staniar, associate professor of equine science; Emily McGaffigan, recently graduated undergraduate student in animal science; and Siera Hall, graduate student in physiology.