What does a positive occult stool test mean?

What a Positive Occult Stool Test Means

A positive occult blood test indicates bleeding somewhere in the gastrointestinal tract and requires follow-up with colonoscopy to identify the source, which could be colorectal cancer, polyps, or other conditions in either the upper or lower GI tract. 1, 2

Sources of Gastrointestinal Bleeding

A positive fecal occult blood test can result from various conditions:

Lower GI Tract Sources

• Colorectal cancer (11% of positive tests) 1
• Adenomatous polyps (37% of positive tests) 1
• Inflammatory bowel disease
• Hemorrhoids
• Anal fissures

Upper GI Tract Sources

• Esophagitis
• Gastric ulcers
• Duodenal ulcers
• Gastritis

Research shows that upper GI tract lesions are actually found more frequently than colonic lesions in patients with positive occult blood tests 3. In one study, 71 patients had upper GI bleeding sources while 54 had colonic sources 3.

Significance and Follow-up

The presence of occult blood is a warning sign that requires proper evaluation:

• Required follow-up: A positive test must be followed by colonoscopy within 3-6 months 2
• Cancer detection: Fecal occult blood testing can reduce colorectal cancer mortality by 15-33% when properly implemented 1
• False positives: Not all positive tests indicate cancer - only about 11% of positive tests reveal colorectal cancer 1

Types of Occult Blood Tests

Different tests have varying sensitivity and specificity:

1. Guaiac-based tests (gFOBT):

   • Lower sensitivity (37-79% for cancer)
   • Higher specificity (86-98%)
   • Affected by diet and medications 1

2. Immunochemical tests (FIT):

   • Higher sensitivity (73.8% for cancer)
   • Better specificity (94.9%)
   • Not affected by diet 2, 4

3. Multitarget stool DNA tests (Cologuard):

   • Highest sensitivity (92.3% for cancer)
   • Moderate specificity (86.6%) 2

Common Pitfalls in Occult Blood Testing

1. Single in-office testing: Testing a single stool sample during a digital rectal exam has extremely low sensitivity (only 4.9% for advanced neoplasia) and should never be used for screening 1

2. Inadequate follow-up: Nearly one-third of physicians incorrectly follow up a positive test with repeat stool testing rather than colonoscopy 1

3. Patient non-compliance: Only 32.8-62.1% of patients complete recommended colonoscopy after a positive stool test 2

4. Delayed follow-up: Delaying colonoscopy beyond 6 months increases the risk of colorectal cancer by 58% and advanced-stage disease by 116% 2

Best Practice Approach

1. Ensure proper test collection (2-3 stool samples collected at home)
2. Avoid NSAIDs, aspirin, and vitamin C before testing
3. Follow up ALL positive tests with colonoscopy, not repeat stool testing
4. Complete colonoscopy within 3-6 months of a positive result
5. If colonoscopy is not possible, use flexible sigmoidoscopy plus barium enema 5

Remember that a negative test does not guarantee absence of colorectal cancer, as only 49% of cancers are identified by initial screening 1. Annual testing is required for continued protection.