UNIVERSITY PARK, Pa. – Researchers from Pennsylvania State University have developed a new method to improve a blood test’s ability to detect inflammation in horses.

Tools and tests to detect inflammation in horses remain limited, Molly Friend, a doctoral candidate in the Intercollege Graduate Degree Program in Integrative and Biomedical Physiology, said in an interview. Typically, veterinarians will quantify inflammation by testing for acute phase proteins in the blood. For horses, the major acute phrase protein is serum amyloid A (SAA). SAA rises very high and very quickly in the bloodstream after horses encounter an inflammatory stimulus, such as an injury, Friend said.

“What’s really popular for veterinarians right now is using the stall-side snap serum amyloid A tests,” she explained. “That allows them to quantify (SAA) in the moment, which is great, but (SAA) is only one of multiple acute phase proteins and only one marker (of inflammation). Because (SAA) is more of an acute inflammatory marker, we were also curious to look at more of the slow-rise and slow-fall acute phase proteins.”

To approach this research interest, the group decided to focus on a blood test called a complete blood count or CBC. CBCs are routinely used by veterinarians to assess the overall health of animals, diagnose and monitor disease progression, and evaluate treatment effectiveness by quantifying 19 measurements, including counts of red and white blood cells. Vets use reference intervals when interpreting information from CBC tests. Reference ranges and intervals are developed through research and represent what a clinically healthy animal’s blood composition would look like.

“While reference intervals are often created from clinically healthy presenting horses, that doesn’t necessarily mean that there’s no inflammation happening behind the scenes,” Friend noted. “That got us looking toward the creation of more inflammation specific reference intervals for each of the blood cell types and beginning to adapt these inflammatory indices that have become popular in human research for horses.”

In human medicine, three inflammatory indices known as the systemic inflammation index (SII), systemic inflammatory response index (SIRI), and the aggregate index of systemic inflammation (AISI) have been developed which use information from CBCs to infer inflammatory information. For example, the SII compares neutrophil (a type of white blood cell that acts as a first responder to inflammation) and platelet counts to lymphocyte (a type of white blood cell that recognize and fight bacteria and viruses) counts, values that are measured in a CBC. In this way, doctors and researchers can learn about someone’s overall inflammatory status, which can help diagnose and monitor certain diseases without more expensive testing.

The researchers completed an observational study in which they drew blood from 199 clinically healthy horses and horses under veterinary care. The horses under veterinary care had a variety of conditions from wounds to gastrointestinal distress, although the nature and duration of inflammation were not characterized specifically as part of the study. Then, the group analyzed the blood for concentrations of SAA and haptoglobin, another acute phase protein.

A variety of statistics were conducted to understand the relationship between CBC outputs and markers of inflammation, Friend explained. In this way, the group was able to quantify the inflammation and tie the values of the three inflammatory indices (SII, SIRI and AISI) to the inflammatory markers studied. New reference intervals were determined for non-inflamed horses which were slightly better at detecting inflammation than the broader industry standard reference ranges.

“I was really excited about our use of these inflammatory indices that have been developed and used in humans and that are starting to creep into the small animal (research) literature, but they’ve only been used in horses in one study before,” Friend said. “Here, we were able to quantify the inflammation and tie the values of these three inflammatory indices – the SII, SIRI, and AISI – to these inflammatory markers. We found that (the inflammatory indices) seem to outperform these individual blood counts alone.”

In other words, understanding the relationship between the concentration of different cells present in the blood can present a broader and clearer picture of inflammation within the body. Characteristic changes in several different population of cells occur alongside inflammation. For example, lymphocytes might be depressed initially during an inflammatory event, while neutrophils increase, Friend added.

“The interplay between these changes might be a more effective way to detect inflammation,” she said.

More research is needed to validate the methods developed by the team, as well as applied to different types and duration of inflammation. Friend hopes that the methodology can become another tool for vets to use to identify inflammation, especially to evaluate chronic and low-grade cases.

Friend recommends that those with horses have a good working relationship with their vets and understand their horse’s “normal.”

“These reference intervals (for blood tests) can be pretty wide, and sometimes horses tend to fall in one area of a reference interval,” she said. “Make sure you know your horse’s normal temperature, heart rate, things of that nature. If you’re able to get a CBC, take a look at it and see where your horse’s normal sits at, because that can be valuable information.”