From the Guidelines
A negative fecal occult blood test (FOBT) result indicates a lower likelihood of colon cancer, but it does not completely rule out the presence of colon cancer or precancerous polyps. This is because FOBTs are designed to detect microscopic amounts of blood in stool that might indicate colorectal cancer or large polyps, but these tests can miss some cancers and many polyps 1. According to the Asia Pacific consensus recommendations for colorectal cancer screening, FOBT, flexible sigmoidoscopy, and colonoscopy are recommended options for CRC screening, with annual or biennial screening with FOBT using a guaiac-based test or an immunochemical test shown to reduce both CRC and CRC-related mortality compared with no screening 1.
The sensitivity of a single FOBT is low, in the range of 30–50%, but repeated annual testing can detect as many as 92% of CRCs 1. It is essential to continue with regular screening according to guidelines based on age and risk factors, even with a negative FOBT result. For average-risk individuals, screening is typically recommended starting at age 45, with FOBT tests performed annually. If you have risk factors such as a family history of colon cancer or personal history of inflammatory bowel disease, more frequent or different types of screening may be needed.
Key points to consider:
- A negative FOBT result does not completely rule out colon cancer or precancerous polyps
- FOBTs can miss some cancers and many polyps
- Regular screening is essential, even with a negative FOBT result
- Screening guidelines vary based on age and risk factors
- FOBT tests should be performed annually for average-risk individuals starting at age 45 1.
From the Research
Definition of a Negative FOBT Result
A negative Fecal Occult Blood Test (FOBT) result indicates that no blood was detected in the stool sample [ 2 ]. However, it is essential to note that a negative result does not entirely rule out the presence of colorectal cancer or other gastrointestinal issues.
Implications of a Negative FOBT Result
- A negative FOBT result may provide false reassurance, as it is not 100% sensitive in detecting colorectal cancer [ 3 ].
- Studies have shown that patients with a false-negative FOBT result may have a higher risk of metastatic disease and increased mortality compared to those with a positive conversion [ 2 ].
- A negative FOBT result should not delay further investigation if symptoms persist or if there is a high suspicion of gastrointestinal bleeding [ 4 ].
Comparison with Other Screening Methods
- Flexible sigmoidoscopy and colonoscopy have been shown to be more effective in detecting colorectal cancer and advanced neoplasms compared to FOBT [ 3 ].
- A systematic review and meta-analysis found that FOBT had poor sensitivity in predicting presumptive causes of iron deficiency anemia and did not support its use in this context [ 5 ].
- A Cochrane review found that both flexible sigmoidoscopy and FOBT reduce colorectal cancer mortality, but the comparative effectiveness of these tests is still unclear [ 6 ].