The SUCCEED Equine Fecal Blood test is a simple stall-side test that uses antibodies to detect two specific components of equine blood in a fresh fecal sample from a horse. Test results help determine if injury – lesions, ulcers, inflammation and the like – exists in the horse’s GI tract and may give some indication of location.
Using Antibodies to Detect Blood Components in Horses’ Feces
The FBT is a colorimetric (color change) test based on the reaction of antibodies to the presence of equine blood components hemoglobin and albumin. Color lines appear on the FBT strips when albumin or hemoglobin are present at levels that fall within a range carefully calibrated to reflect true pathological conditions.
What Are Antibodies
Antibodies are Y-shaped protein molecules secreted by specific white blood cells. Antibodies are an important part of human and animal immune systems because they identify and “flag” foreign objects, called antigens, allowing other parts of the immune systems to attack and destroy the foreign object.
The tip of antibody molecules, known as the antigen binding site, vary widely in structure. This allows for the creation of a large number of variations for binding to specific antigens. We can then develop unique antibodies that bind only to specific antigens – which makes antibody tests possible.
How Antibodies Are Used in the FBT
The FBT uses three types of antibodies created specifically for the test:
- one that attaches to equine albumin,
- one that attaches to equine hemoglobin,
- one that attaches to the antibody markers used in the test and creates the control line.
In the FBT test cassette, the antibodies are also attached to a dye which creates the magenta line that appears with a positive test result in the presence of equine albumin or hemoglobin.
Albumin as an Indicator of Hindgut Injury in Horses
Albumin is a protein that is free-floating in blood plasma. While it is present any time there is a bleeding injury, it may also be released through smaller injuries that only seep plasma.
Additionally, albumin is digested by bile and proteolytic enzymes, such as pepsin and trypsin, in the small intestine. As a result, albumin present in a horse’s feces would have originated from a source caudal (after) the common bile duct, primarily the colon. Thus, fecal albumin is a good indicator of hindgut lesions or ulcers.
Hemoglobin in Feces as an Indicator of GI Injury in Horses
Hemoglobin is a protein that is bound up in red blood cells. As a component of red blood cells, it is always present any time there is an injury that produces whole blood.
While hemoglobin may be somewhat degraded in the digestive process, it is at a much lower rate than albumin. Whereas albumin is broken down and digested in the small intestine, hemoglobin may be digested by bacteria in the hindgut. When bleeding occurs in a horse’s gut, some of the blood is degraded, leaving the rest to move through the digestive tract until it is expelled in the horse’s feces. Therefore, hemoglobin in a horse’s feces could have originated from anywhere within the GI tract. Because it is present only with active vascular bleeding, a hemoglobin positive indicates a lesion with a severity equivalent to grade 2 or higher ulceration.
Results for Albumin and Hemoglobin Taken Together May Differentiate Fore, Hind, or Both
When results for albumin and hemoglobin are used together, veterinarians have a useful tool to help determine whether the source of injury is in the horse’s foregut, hindgut, or both. Here’s what the combination of results shows:
- Positive for albumin only represents an injury in the hindgut only.
- Positive for hemoglobin only represents a bleeding injury in the foregut only.
- Positive for both hemoglobin and albumin indicates a definite hindgut condition, and a potential foregut condition. (Gastric scoping can help rule in or rule out gastric ulceration in this case.)
- Negative for both hemoglobin and albumin generally indicates no hindgut condition, and no foregut conditions equivalent to grade 2 or higher. However, a low-grade foregut condition, such as a grade 1 gastric ulcer is still possible. Also keep in mind that ulcers can bleed intermittently, or if the damage is so severe that the tissue has died, won’t bleed at all.
Learn more about how to apply these results in light of a veterinarian’s full diagnostic work-up. Also, be sure to keep in mind these limitations of equine fecal blood testing.