Globin is the protein component of hemoglobin, the molecule within red blood cells responsible for transporting oxygen throughout the body. When bleeding occurs anywhere in the digestive system, this protein enters the gastrointestinal tract and passes into the stool. Fecal globin refers to this specific protein when it is detected in a stool sample. Its presence indicates blood loss occurring somewhere along the digestive pathway, a condition often referred to as occult, or hidden, blood in the stool. Detecting this protein is the target of a widely used, non-invasive screening method designed to identify potential issues within the lower digestive tract.
The Purpose of Fecal Immunochemical Testing
The Fecal Immunochemical Test (FIT) uses antibodies to specifically target and detect the human globin protein in stool samples. This targeted approach represents an advancement over older screening methods, which were prone to interference from foods like red meat or certain vegetables. Because the FIT is highly specific to human globin, it requires no special dietary or medication restrictions prior to collecting the sample.
The test focuses on globin due to its fragility during the digestive process. Globin protein is rapidly broken down by digestive enzymes present in the stomach and small intestine. Therefore, if globin is found intact in the stool, it suggests the blood loss originated in the lower gastrointestinal tract, specifically the colon or rectum. This mechanism allows the FIT to act as an effective screening tool primarily for conditions affecting the large intestine. The test’s ability to detect blood that is not visible to the naked eye is important for catching potential issues early.
Understanding Elevated Globin Levels
A positive result on a fecal immunochemical test indicates an elevated level of globin, signifying blood loss in the lower digestive tract. While this finding is not a diagnosis, it serves as a reliable marker that requires further investigation. The presence of blood in the stool can be caused by various conditions.
The primary reason for screening is the potential detection of advanced adenomas (large precancerous polyps) or colorectal cancer. These lesions often have fragile blood vessels that bleed intermittently as stool passes, releasing globin into the feces. Other non-cancerous conditions can also cause a positive test result, including:
- Hemorrhoids
- Anal fissures
- Diverticulitis
- Inflammatory bowel disease, such as Crohn’s disease or ulcerative colitis
A positive result identifies a need to locate and identify the exact cause of the bleeding.
Necessary Follow-Up Examinations
Following a positive fecal immunochemical test, the next action is to undergo a diagnostic examination, typically a colonoscopy. The FIT is a screening tool, designed only to flag the presence of hidden blood, and cannot determine the cause or location of the bleeding. The colonoscopy is the second step because it transforms the screening result into a definitive diagnosis.
During a colonoscopy, a physician uses a flexible tube equipped with a camera to examine the entire lining of the colon and rectum. This allows for direct visualization of the intestinal wall to find the source of the globin. If polyps are discovered, they can usually be removed immediately during the procedure, preventing them from developing into cancer. Timely follow-up after a positive test is recommended because delays may increase the risk of finding more advanced disease.