What type of stool exam is used to check for bleeding?

Fecal Immunochemical Test (FIT) Is the Preferred Stool Exam for Detecting Gastrointestinal Bleeding

The fecal immunochemical test (FIT) is the preferred stool examination for detecting gastrointestinal bleeding due to its superior sensitivity, specificity, and lack of dietary restrictions compared to other stool tests. 1, 2

Types of Stool Tests for Detecting Blood

Fecal Immunochemical Test (FIT)

• FIT specifically detects human hemoglobin in stool, making it highly specific for human blood 1, 2
• Does not require dietary restrictions before testing, improving patient compliance 3, 2
• More sensitive and specific than guaiac-based tests for detecting lower gastrointestinal bleeding 4, 2
• Recommended by the US Preventive Services Task Force for colorectal cancer screening in adults aged 45 years and older 1

Guaiac-based Fecal Occult Blood Test (gFOBT)

• Based on chemical detection of blood in stool 1
• Requires dietary restrictions (avoiding red meats, certain vegetables, vitamin C, and NSAIDs) before testing 1, 3
• Less sensitive and specific than FIT 1, 3
• Can detect blood from both upper and lower GI tract, potentially leading to false positives for lower GI bleeding 3
• High-sensitivity gFOBT is still recommended as an option for colorectal cancer screening 1

Stool DNA Test (sDNA-FIT)

• Combines FIT with detection of DNA biomarkers for cancer in cells shed from the colon and rectum 1
• Higher sensitivity for detecting colorectal cancer than FIT alone but requires more follow-up colonoscopies 1
• Currently available as multitarget stool DNA test (includes FIT component) 1
• Recommended screening interval is longer (1-3 years) compared to annual FIT 1

Clinical Application and Follow-up

When to Use Stool Tests for Bleeding

• Recommended as part of colorectal cancer screening for average-risk adults aged 45 years and older 1
• Useful in evaluating patients with iron deficiency anemia of unknown origin 5
• Can be used to evaluate occult gastrointestinal bleeding when the source is unclear 1

Follow-up of Positive Results

• Any positive stool test for blood requires follow-up with colonoscopy 1, 6
• If complete colonoscopy cannot be performed, flexible sigmoidoscopy with air-contrast barium enema is the next best alternative 6
• For patients with persistent bleeding and negative colonoscopy, upper endoscopy should be performed to evaluate for upper GI sources 1

Limitations and Considerations

FIT Limitations

• Cannot reliably distinguish between upper and lower GI bleeding sources 3
• Has limited value as a screening test before capsule endoscopy in obscure GI bleeding (sensitivity 63%, specificity 61%) 7
• May miss intermittent bleeding sources 1

Special Considerations

• Single stool sample collected during digital rectal examination is not recommended due to poor sensitivity 1
• Specimens should be collected from successive bowel movements over multiple days for optimal sensitivity 1
• For active, visible bleeding, direct visualization tests (colonoscopy, CT angiography) are preferred over stool tests 1

Algorithm for Selecting Appropriate Stool Test

1. For colorectal cancer screening in average-risk adults: Use FIT annually or sDNA-FIT every 1-3 years 1
2. For evaluation of suspected occult GI bleeding:
   • Start with FIT due to higher sensitivity and no dietary restrictions 2
   • If positive, proceed to colonoscopy 6
   • If negative but clinical suspicion remains high, consider upper endoscopy 1
3. For active, visible bleeding:
   • Skip stool tests and proceed directly to colonoscopy or CT angiography based on hemodynamic status 1

By following this evidence-based approach to stool testing for gastrointestinal bleeding, clinicians can optimize detection while minimizing unnecessary procedures and patient inconvenience.