Tina Holberg Pihl, DVM, PhD, associate professor of medicine and surgery at the University of Copenhagen’s Department of Large Animal Sciences, performed the study in collaboration with practitioners at the University of Pretoria, in South Africa. She presented her results at the 2017 International Equine Colic Research Symposium, held July 18-20, in Lexington, Kentucky.
“We wanted to see if acute phase proteins are adding something to what we are already looking at,” she said. “We don’t need another test (if it’s not useful).”
Pihl explained that APPs are elevated in horses with severe colic, and researchers already know there’s an association between blood APP concentrations and survival. “Larger studies evaluating the prognostic value of APPs are, however, lacking,” she said. “I wanted to see if serum amyloid A and haptoglobin in blood and peritoneal fluid and fibrinogen (in blood) could give a prognosis in these horses.”
First, here’s a quick primer on these liver-produced proteins:
Haptoglobin binds with hemoglobin, a protein inside red blood cells that’s released when red blood cells are destroyed (a normal part of their life cycle). If the destruction of red blood cells outpaces production, haptoglobin levels drop because the liver can’t keep up. Haptoglobin production in the liver increases slowly in response to acute inflammation.
Serum amyloid A (SAA) helps the immune system fight infection early in the course of disease. Levels are either undetectable or very low in normal, healthy horses, but they can rise 100 to 1,000 times higher than baseline in horses fighting an inflammatory condition.
Fibrinogen plays a major role in blood clotting and functions in the inflammatory process by converting to fibrin, which serves to localize an invasive disease process. Levels generally rise in sick horses.
Pihl and her team included 551 horses admitted with acute colic signs at the University of Copenhagen and the University of Pretoria. Veterinarians collected blood samples and/or peritoneal (abdominal cavity) fluid from the horses, freezing the samples and sending them for automated testing.
They did not include horses with inflammation unrelated to the abdomen—for example, one horse had a large wound—and, ultimately, they excluded 87 horses that didn’t meet study criteria. Thirty-nine percent required surgery, and 20% of those horses did not survive to hospital discharge.
It turned out that SAA in serum and peritoneal fluid and haptoglobin in peritoneal fluid were the only test results significantly associated of nonsurvival. Ultimately, the researchers optimized a predictive model for nonsurvival that includes a combination of serum SAA, plasma fibrinogen, mucous membrane color, body temperature, gastric reflux greater than 5 L, plasma lactate, hematocrit, and peritoneal fluid hemolysis (red blood cell destruction).
“Measuring acute phase proteins at admission can improve the ability to classify the horses as survivors and nonsurvivors,” she said. “Serum amyloid A measured in the blood performed the best of the acute phase proteins. Measuring SAA in serum can improve the ability to predict prognosis in horses with acute colic as survivors or nonsurvivors.”