APP in Veterinary Medicine

APP are commonly increased with trauma, infection, stress, neoplasia, and inflammation. The goal of the APR is to maintain homeostasis and promote healing. APP aid in the promotion of leukocytosis, complement activation, opsonization, clotting, and protease inhibition.

There are over 200 APP but with dominant markers in different species. C-reactive protein (CRP) is a major APP of humans and dogs. Serum Amyloid A (SAA) is a major marker of horses. Baseline or negligible levels of these proteins are present in normal animals. With appropriate stimulus, increases range from 10-100 fold. With resolution, the APP can decrease to normal range within 24-48 hours.

APP have been well described in human medicine beginning with the identification of CRP in the early 1930s. CRP is now known as a major marker of infection, autoimmune disease, trauma, and malignancy. It is commonly used as a marker of myocardial infarction in humans. Recommendations have been made to add this APP to an annual blood work panel because of its sensitivity for subclinical disease.

APP have also been extensively studied in animal species where similar applications have been observed. In dogs, CRP has been observed to increase with surgery and post surgery complications, joint disease, pancreatitis, IBD, and a variety of infectious agents. Increases in CRP are not directly correlated to increases in WBC and increases will offer occur prior to a WBC count increase and decreases will occur with disease resolution prior to WBC normalization. In horses, SAA has been observed to increase with colic, bacterial infection, joint disease, and surgery and post surgery complications. Other studies have detailed the application of APP to cats, chickens, cows, mice, nonhuman primate, sheep, pigs, and many zoo species.

Many commercial assays have been validated for use in companion, large, and non-domesticated mammals. In addition, some point of care analyzers are also available but most often host reagents which specific to certain species (dog, horse). Be aware of this issue when requesting APP testing. A growing body of literature is now available documenting the use of APP in a myriad of special species from rabbits to dolphins to elephant. At this time, due to the lack of cross reactive reagents, protein electrophoresis is recommended over APP testing for most avian, reptile, and fish species.

While APP may not be diagnostic of particular diseases, they have been demonstrated to be valuable prognostic markers. In addition, they are an important part of routine blood work and as markers of herd health. It should be noted that APP are not a replacement for other testing including the complete blood count but recognized that these measures all have different timelines of expression and normalization. Major APP increase and decrease quickly which provides advantages for acute onset conditions and for monitoring for response to treatment.