TheHorse.com caught up with two veterinarians well-versed on the topic—Luis Castro, DVM, a racehorse practitioner with Teigland, Franklin & Brokken in Boynton Beach, Florida, Saratoga Springs, New York; and David Levine, DVM, Dipl. ACVS, staff surgeon at New Bolton Center, the large-animal hospital of the University of Pennsylvania School of Veterinary Medicine, in Kennett Square, Pennsylvania—to find out more about this important biomarker.
TheHorse.com: First, the burning question: What is SAA?
Dr. Luis Castro: Serum amyloid A. It’s a biomarker protein produced in the liver in the face of inflammation caused by infection.
Dr. David Levine: SAA has several roles in inflammatory processes, but most importantly for us it serves as a marker for inflammation that increases and decreases quickly so it can give us real-time information using a blood test.
TH.com: Is SAA found in healthy horses’ blood?
Levine: SAA is found in very low quantities in normal horses. It is not secreted until inflammation occurs.
TH.com: When does the horse’s body produce excess SAA, and what would elevated SAA levels indicate to a veterinarian?
Castro: In the face of infection SAA levels begin to rise almost immediately. The response is faster than (other abnormal values we’d look for on) most complete blood counts1 and fibrinogen (a biomarker we have been using for decades) levels. It is extremely sensitive to onset, duration, and the end of the disease process.
Levine: There is still much to be learned about SAA, but we do know that it increases in response to inflammation and veterinarians can test for this increase using a simple blood test. It can be followed to see response to treatment, as SAA changes rapidly in the bloodstream and can indicate whether a particular treatment is effective.
TH.com: Why should veterinarians, horse owners, and trainers be familiar with SAA?
Castro: It is extremely useful in determining the presence of infection at a very early stage. It would allow not only earlier treatment but can monitor whether the treatment is working and when the proper time to end treatment would be. All this can be determined immediately, and stall-side.
Levine: SAA is more timely compared to fibrinogen, which is our current gold standard test for inflammation. When you look at fibrinogen you are often looking at the inflammatory picture with a 3-day lag period. That is less helpful when trying to determine if you treatment is effective and whether your horse is responding appropriately.
TH.com: Dr. Castro, are you currently using SAA evaluation in your practice?
Castro: Yes, very much so. We test and monitor horses with fevers, diarrhea, horses that scope with mucus in their trachea, horses with cellulitis (a bacterial infection of the skin and associated tissues) or edema (fluid swelling) in a leg, horses with joint effusion (swelling) and severe lameness. I use it in instituting treatment for any infection, as well as monitoring whether or not that treatment is working.
TH.com: Dr. Levine, what is still unknown about SAA testing, what have you studied, and what are you hoping to study in the future?
Levine: We are still trying to determine which inflammatory conditions increase SAA. We know that infectious inflammation can cause an increase in SAA but are not sure what to expect from different conditions. For example, does SAA go up after different surgical procedures, does SAA increase during colic? Will that help determine medical vs. surgical colic? Does SAA definitively differentiate between inflammation that is infectious vs. noninfectious?
Several SAA studies have been done and are currently underway. We are trying to ultimately find out if SAA can be used to detect infection early after orthopedic and colic surgeries. It would also be nice to use SAA as a screening test for patients that are going to surgery to see if there are underlying inflammatory conditions that make it a higher risk.
TH.com: Dr. Castro, what research would you like to see carried out regarding SAA levels in horses?
Castro: I would like to see how quickly, post-infection, the levels rise. Although the response is faster than anything we’re using today, there appears to be a slight lag. I would like get a better idea of time, although I believe it seems to be in hours.
TH.com: Do you think veterinarians will employ SAA testing more frequently in the future, and why?
Castro: Yes. It’s accurate, fast, simple, and relatively inexpensive. It’s another piece of the puzzle that can guide us to optimized treatment.
Levine: Yes. The new stall-side test makes this test more accessible and, as the data comes out on its uses, it will be employed more often even in field conditions.
TH.com: In your opinion, what’s the most important thing about SAA for people to remember?
Castro: It’s a wonderful tool that we personally have come to rely on with regards to optimizing and differentiating treatment options, but it doesn’t take the place of a good physical exam, blood work, and complete clinical evaluation.
Levine: SAA can be used like other diagnostic tests to give more data on the overall clinical picture. It shouldn’t be used on its own without a complete history, physical exam, and other diagnostics. It does, however, give accurate and real-time data on the inflammatory picture of the horse. As further research is done, it will be a valuable diagnostic test within our armamentarium.
1 Anhold, H et al. A Comparison of Elevated Blood Parameter Values in a Population of Thoroughbred Racehorses. Journal of Equine Veterinary Science. 2014 May;34(5):651–655.