APP Testing in Companion Animals

In other species including humans, these markers have been well shown to have prognostic value as well as a key test in a routine wellness exam. Of note, APP levels rarely have a high correlation with traditional measures like white blood count as these different components of the acute phase response have varying timelines for response.

Whereas a single analysis of a major acute phase protein does not predict case outcome in serious cases, serial measurements indicating the presence of continued high levels of this biomarkers are correlative with a negative outcome.

APP in Dogs

Like humans, the major acute phase protein (APP) in dogs is C-reactive protein (CRP). In normal animals, CRP is expressed at negligible levels. A new reagent has become available to measure serum amyloid A (SAA) in dogs. Like CRP, SAA is a major APP. The magnitude of change was observed to be much higher with disease in clinically abnormal dogs. CRP is a valid prognostic marker in several specific conditions including IBD, renal disease, infection, and neoplasia and arthritis.

APP in Cats

SAA is a major APP in the cat. It has been observed to increase in neoplasia, thyroid disease, pancreatitis, and diabetes in addition to various infectious process (pyometra, FIP). As observed in other species, SAA has key value as a prognostic marker.

APP in Horses

SAA is a major acute phase protein which is synthesized in the liver as part of the acute phase response. It is considered to be part of the first line of defense in response to inflammatory stimuli including trauma, stress, infection, neoplasia, and inflammation. A growing veterinary literature has shown its utility as part of an annual wellness exam and sensitivity for prognostic value in disease states. We have validated this assay in our laboratory and determined in-lab reference intervals.

Summary of an in-house laboratory study [JAVMA (243:113-119, 2013)]:

Samples from 212 horses from a specialty veterinary practice were examined using measures including CBC, fibrinogen, serum protein electrophoresis, and SAA.

• Versus mild (<2 fold) increases in total WBC and fibrinogen, marked 75-fold mean increases in SAA were present in clinically abnormal horses with a range of diseases.
• SAA was present in neglible levels (<10mg/L) in normal animals.
• Levels in excess of 1000mg/L were routinely observed in animals with severe inflammatory processes related to infection.
• SAA had the highest diagnostic accuracy for the detection of inflammation.
• SAA was the most reliable indicator of a patient’s return to health.SAA has been demonstrated to act as a major acute phase protein in horses. Increases are detectable within 24 hours of stimulation and, given its short half-life, significant decreases rapidly occur with a positive response to treatment.