Does your practice routinely use serum amyloid A (SAA) testing and, if so, how? Are you looking to implement this test into your toolbox but aren’t sure how to go about it? Two internal medicine veterinarians answered these questions during a Table Topic discussion at the 2018 American Association of Equine Practitioners convention, held Dec. 1-5, in San Francisco, California.
Nicola Pusterla, DVM, PhD, Dipl. ACVIM, professor of medicine and epidemiology at the University of California, Davis, School of Veterinary Medicine, and Laura H. Javsicas, VMD, Dipl. ACVIM, of Rhinebeck Equine LLP, in New York, co-mediated the session. They kicked it off with a brief review of SAA basics.
What is SAA?
Pusterla quickly reminded attendees that SAA—referred to as an acute-phase protein produced by the liver—essentially acts as a marker of inflammation. He highlighted the fact that while SAA is a powerful indicator that inflammation is present, the test can’t tell you what’s causing the inflammation or, importantly, where it is.
“Infection, trauma, neoplasia (tumors), and more can all cause inflammation,” Pusterla said. “Together with a complete physical examination and other routine diagnostic blood tests, SAA can provide powerful real-time information about whether treatment/intervention is required, whether the inflammation is improving or getting worse during treatment, and even when treatment should be discontinued.”
While most practitioners attending the session said they use SAA regularly, how they apply the test varies markedly depending on the type of practice. Pusterla, Javsicas, and veterinarians in the audience listed examples of how they’ve used SAA in everyday equine practice:
- Differentiating between equine asthma and other upper respiratory conditions (bacterial or viral). In the former, SAA should be 0, whereas it will likely be elevated in association with infectious causes.
- Differentiating guttural pouch disease (usually caused by bacteria) from inflammatory airway disease (lower airway inflammation, caused by allergies, bacteria, or viruses) in young racehorses as potential causes of poor performance.
- Intensive, time-consuming colic cases that are notoriously expensive to treat. If SAA levels start to decrease from 2,000 to 1,000—suggesting that the inflammation is subsiding, and the case is likely moving in a positive direction—this information might help owners make the decision to forge ahead with costly treatment to ultimately save the horse.
- In healthy horses either pre-surgically (e.g., for osteochondritis dissecans or chip fracture removal) or during a prepurchase examination. Knowing a horse’s SAA value when he’s healthy provides a baseline should he become ill in the future.
- Routine screening in neonatal foals to potentially predict a health issue. This seemed particularly useful on farms that regularly deal with Rhodococcus equi in foals. In addition to daily temperature checks, if the SAA values began to elevate, veterinarians pursued further diagnostics and prescribed antibiotics for the foals, rather than treating all foals prophylactically.
- Following transport (to help identify horses that might need to be isolated at their destinations) and before transport; SAA was deemed particularly useful for horses considered at high risk for infection—those that are highly competitive and stressed or that were recently ill—to help decide whether they have recovered sufficiently to handle shipping stress.
- During disease outbreaks such as influenza and equine herpesvirus, even in healthy horses, to better control the outbreak and group or isolate horses appropriately.
What Do the Results Mean?
As for specific SAA numeric values and what they mean, Pusterla said, “The kinetics of inflammation vary so immensely between different disease processes, so it’s hard to say what a ‘significant’ increase or decrease is.”
Instead of relying on an exact SAA numeric value as an indicator of a clinical problem, Pusterla said he looks to trends. For example, he starts “getting nervous” with levels higher than 1,000 and will continue to monitor SAA values to assess that horse’s response to therapy.
During the session Pusterla pointed out the importance of not becoming reliant on a single diagnostic test, even one as black-and-white as SAA. In addition, he recommended veterinarians read the manual before using this stall-side test and have all the equipment they need before starting, including extra batteries, lens cleaners, and swabs. When monitoring a single patient’s SAA levels, use the same type of sample each time (for example, whole blood), and follow the manufacturer’s recommendations for performing the test.