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SAA in horses: a useful screening tool for infections – May 2017

May 15, 2017

SAA in horses: a useful screening tool for infections

Cordelia Francis BVSc MRCVS

Serum Amyloid A (SAA) is an “acute phase protein”, which is a collective term for proteins that are produced and released by the liver in response to inflammation. It is a useful marker for several reasons. Firstly SAA levels increase very rapidly in response to infection, often within 24 hours, which is helpful for making an early diagnosis. Secondly there is a huge pathologic range; normal horses have blood SAA concentrations very close to 0 mg/L and with inflammation it can rise to >3000 mg/L. This large range allows us to “grade” the severity of inflammation and can also be used to monitor the horse’s response to treatment.

SAA measurements can also be helpful in differentiating between diseases that have similar clinical signs but very different treatments. For example, a painful, swollen joint can be due to either a traumatic synovitis or a septic arthritis. Traumatic synovitis is inflammation of the joint due to injury but without infection, similar to a joint sprain in humans. Septic arthritis is inflammation of the joint caused by infection (i.e. the presence of bacteria). In the early stages these two diseases can look very similar but we can use the horse’s SAA levels to help distinguish between them. We can measure SAA levels in either blood or joint fluid samples. When there is an infection present the SAA levels are usually dramatically increased, where as they only increase mildly in traumatic synovitis. This can help us make an early diagnosis, allowing appropriate treatment and thereby improving the prognosis.

We routinely measure blood SAA levels in sick horses as any generalized infection will cause an increase, not just joint infections. Because the SAA kit we use at MVS is portable we are able to measure SAA levels both at the clinic and on the farm.