Why can't occult blood tests using anti-hemoglobin detect bleeding that originates in the esophagus?

• A. The hemoglobin is degraded by the time of excretion and is not recognized by the antibody.
• B. The K-ras gene will be degraded by bacteria.
• C. The dye used in the test cannot detect intact red blood cells.
• D. Urobilinogen and bilirubin in the intestines will interfere with the test

Answer: (A)

Anti-hemoglobin occult blood tests rely on antibodies that bind to intact human hemoglobin present in the stool. Blood from the esophagus or other upper GI sources is exposed to stomach acid and digestive enzymes as it passes through the GI tract. These conditions degrade hemoglobin into fragments, so by the time the blood is excreted, the antibody may no longer recognize it. That degradation means an upper GI bleed can yield a negative test even when bleeding is present. In short, intact hemoglobin is needed for detection, and upper GI blood is often broken down before excretion.