Serum Amyloid A: An Effective Tool for Diagnosing, Monitoring Infections

Synovial infections affect joints and tendon sheaths, often leading to lameness. A rapid test to detect these infections can be lifesaving. Using the same test to monitor disease progression and potentially change the course of treatment when needed would be invaluable. German veterinary researchers say that serum amyloid A (SAA) fits this profile.^*

Defined as an acute phase protein, SAA is produced by the liver in the face of inflammation. SAA levels are nearly zero in the blood of healthy horses and can increase rapidly in response to inflammation, including infection. The half-life of SAA is short, which means it returns to low baseline levels quickly once inflammation has resolved.

“SAA is well suited for the real-time monitoring of disease activity because SAA levels accurately reflect the severity of inflammation. The effect of treatment can also be observed by evaluating the course of SAA,” explained the researchers.

To demonstrate how useful SAA can be for detecting and monitoring synovial infections, medical records of 55 horses presented to a veterinary hospital with injuries less than 24 hours old were reviewed. Twenty-six of those injured horses had evidence of synovial involvement (joint or tendon sheath). The remaining 29 horses had lacerations and trauma but no synovial involvement. All horses underwent standard treatments for their injuries, such as lavage, debridement, bandaging, and postoperative pain control and antibiotics. All horses also had SAA values measured on admission, 12 hours after admission, and then daily until 18 days after admission.

“As expected, SAA levels increased abruptly in the injured horses regardless of synovial involvement. But, horses that did have damage and infection of a synovial structure had higher levels of SAA. In both groups of horses, SAA levels peaked 48 hours after admission,” explained Catherine Whitehouse, M.S., a Kentucky Equine Research nutrition advisor.

After the 48-hour time point, SAA values declined steadily in both groups until 10-12 days after admission. While SAA remained at baseline levels in the group of horses without synovial infections, the SAA levels of three horses being treated for infected synovial structures spiked on days 10 to 12. These horses underwent additional treatments for resurgence of synovial infections.

In this study, SAA proved useful in three ways:

• SAA accurately detected inflammation in all horses;
• SAA helped identify recurrence of infection and the need for additional therapy; and
• SAA helped identify when antibiotics could be stopped in the horses whose SAA values returned to baseline levels.

As part of a treatment plan, horses with soft tissue traumas are often kept on stall rest, which is another management factor to consider.

“Horses placed on stall rest require diet modifications to balance energy status and temperament while ensuring optimal nutrient intakes. Specialty supplements such as Triacton and Synovate HA provide key nutrients to support bone and joint health in horses on stall rest and those with joint and soft tissue injuries,” Whitehouse said.

 ^*Müller, A.-C., K. Büttner, and M. Röcken. 2022. Using systemic serum amyloid A as a biomarker for synovial structure infections in horses with acute limb wounds. Veterinary Record 191(2):1841.