From the Guidelines
Blood in stool tests, also known as fecal occult blood tests (FOBTs), are screening tools used to detect hidden blood in the stool that isn't visible to the naked eye, and the most recent evidence suggests that the fecal immunochemical test (FIT) is the preferred method due to its higher specificity for human blood and lack of dietary restrictions 1. When considering testing for blood in the stool, several options are available, including the guaiac-based FOBT (gFOBT) and FIT.
- The gFOBT requires dietary restrictions before testing, such as avoiding red meat, certain vegetables, and some medications.
- The FIT, on the other hand, does not require dietary restrictions and is more specific for human blood. For either test, small stool samples need to be collected as directed in the kit instructions, typically from multiple bowel movements. These tests are primarily used to screen for colorectal cancer and should be performed annually if this is the chosen screening method. A positive result does not necessarily mean cancer is present but indicates that further testing, usually a colonoscopy, is needed to determine the source of bleeding. The tests work by detecting hemoglobin or other blood components in the stool, which may be present due to bleeding from polyps, cancer, or other conditions affecting the digestive tract. If over 45, regular colorectal cancer screening is recommended, and these stool tests are one option among several screening methods, with the FIT being the most recently recommended method 1. Key points to consider when choosing a screening method include the test's sensitivity and specificity, as well as the patient's individual risk factors and medical history. In cases of suspected lower gastrointestinal bleeding, diagnostic colonoscopy is the preferred diagnostic procedure, with a diagnostic accuracy ranging from 72 to 86% 1. Overall, the choice of blood in stool test should be based on the most recent evidence and individual patient factors, with the FIT being a preferred method due to its higher specificity and lack of dietary restrictions 1.
From the Research
Blood in the Stool Tests
- Blood in the stool can be an indication of various gastrointestinal issues, and several tests can be used to diagnose the cause of bleeding, including:
- Fecal occult blood test (FOBT) to detect hidden blood in the stool 2, 3
- Colonoscopy to visualize the colon and rectum 4, 5, 2, 3
- Esophagogastroduodenoscopy (EGD) to visualize the upper gastrointestinal tract 5, 2, 3
- Capsule endoscopy to visualize the small bowel 2, 3
- Computed tomography (CT) angiography to locate the site of bleeding in patients with hemodynamic instability 4
Diagnostic Approach
- The initial assessment of patients presenting with acute lower gastrointestinal bleeding should include a history of co-morbidities and medications, hemodynamic parameters, physical examination, and laboratory markers 4
- A risk score can be used to aid in decision-making, but should not replace clinician judgment 4
- In patients with occult gastrointestinal bleeding, a stepwise evaluation can identify the cause of bleeding in the majority of patients, starting with EGD and colonoscopy 3
- If a cause is not found after EGD and colonoscopy, capsule endoscopy or deep enteroscopy may be used to further investigate the small bowel 3
Management
- The management of patients with acute lower gastrointestinal bleeding depends on the severity of bleeding and the presence of co-morbidities, such as cardiovascular disease 4
- A restrictive red blood cell transfusion strategy may be used in hemodynamically stable patients, with a hemoglobin threshold of ≤7 g/dL prompting transfusion 4
- In patients with major acute lower gastrointestinal bleeding, colonoscopy should be performed during their hospital stay, and computed tomography angiography may be used to locate the site of bleeding in patients with hemodynamic instability 4