From the Guidelines
For a positive fecal occult blood test (FOBT), the primary recommendation is to proceed with a colonoscopy as soon as possible, ideally within 8-10 weeks, to identify the source of bleeding and prioritize the prevention of colorectal cancer. This approach is based on the understanding that occult blood can indicate various conditions ranging from benign causes like hemorrhoids to more serious conditions such as colorectal cancer, and visual inspection with biopsy capability is necessary for definitive diagnosis 1.
Key Considerations for Colonoscopy
- The colonoscopy should be a complete examination of the entire colon, as bleeding can originate from any part of the lower gastrointestinal tract.
- Prior to the procedure, patients should follow standard colonoscopy preparation, which typically includes a clear liquid diet for 24 hours before the procedure and consumption of a bowel preparation solution to cleanse the bowel.
- Patients should temporarily discontinue blood thinners like warfarin, clopidogrel, or direct oral anticoagulants before the procedure, following their physician's guidance.
- Iron supplements should also be stopped 7 days prior as they can interfere with visualization.
Rationale for Colonoscopy
The recommendation for colonoscopy following a positive FOBT is supported by guidelines from the American Cancer Society, the US Multi-Society Task Force on Colorectal Cancer, and the American College of Radiology, which emphasize the importance of detecting and preventing colorectal cancer 1. These guidelines suggest that tests that can detect both early cancer and adenomatous polyps, such as colonoscopy, should be encouraged if resources are available and patients are willing to undergo an invasive test.
Importance of Test Sensitivity
The choice of screening test is crucial, and tests with high sensitivity for detecting colorectal cancer are preferred 1. The guidelines recommend selecting stool blood tests that have been shown to detect the majority of prevalent CRC in an asymptomatic population. If there is no evidence that an available test has met this benchmark, it should not be offered to patients for CRC screening.
Conclusion is not allowed, so the answer just ends here.
From the Research
Recommendations for Positive FOBT
The following are recommendations for individuals with a positive Fecal Occult Blood Test (FOBT) result:
- A colonoscopy is recommended to examine the entire colon and rule out the presence of cancer or advanced neoplasia 2, 3, 4
- Individuals with positive FOBT results, especially those with high quantitative test results, should be encouraged to undergo a colonoscopy 2
- A program of annual FOBT plus flexible sigmoidoscopy every 5 years is a preferred option for screening the asymptomatic, average-risk population for colorectal cancer 5
- Combining annual FOBT with periodic flexible sigmoidoscopy seems to be an especially effective screening option 5
Follow-up and Diagnostic Evaluation
- Complete diagnostic evaluation, including colonoscopy or flexible sigmoidoscopy with double contrast barium enema, is necessary after a positive FOBT result 3
- The percentage of positive FOBTs followed by complete diagnostic evaluation within 1 year has increased over time, from 57-64% in 1993-1996 to 82-86% in 2000-2005 3
- Adherence to recommendations for complete diagnostic evaluation after a positive FOBT has greatly improved over time in an integrated group medical practice 3
Test Characteristics and Effectiveness
- The sensitivity and specificity of FOBT for detecting colorectal cancer and large polyps vary, with immunochemical FOBT (iFOBT) showing higher sensitivity than guaiac FOBT (gFOBT) 4, 6
- The use of gFOBT or iFOBT is associated with a reduction in colorectal cancer mortality, with relative risk reductions of 13% and 16% in two randomized controlled trials 4
- FOBT has a low sensitivity for polyps, especially smaller ones, and a relatively low specificity, resulting in many false-positive screens 5