What is the recommended protocol for using the fecal globin test (FGT) for colorectal cancer screening?

Recommended Protocol for Fecal Globin Test (FGT) in Colorectal Cancer Screening

For colorectal cancer screening in average-risk adults aged 50-75 years, annual fecal immunochemical testing (FIT) is recommended as one of the preferred stool-based screening options, with collection of two samples from each of three consecutive stools and follow-up colonoscopy for any positive result. 1

Overview of Fecal Blood Testing Options

Stool-based tests for colorectal cancer screening fall into two main categories:

• Guaiac-based fecal occult blood tests (gFOBT): Detect blood through pseudoperoxidase activity of heme/hemoglobin 1

  • Requires dietary restrictions during testing (avoid red meat, certain vegetables, vitamin C) 1
  • Demonstrated mortality reduction in randomized controlled trials 1
  • Lower sensitivity compared to newer tests 1

• Fecal immunochemical tests (FIT): React specifically to human globin 1

  • No dietary restrictions required 1
  • Improved sensitivity compared to gFOBT 1
  • More specific for lower gastrointestinal bleeding 1

Recommended Protocol for Fecal Globin Testing

Patient Selection

• Average-risk adults aged 50-75 years 1
• For those with family history of colorectal cancer or adenomatous polyps, earlier screening may be warranted 1
• Adults aged 76-85 who have been previously screened may have small benefit 1

Test Administration

• For gFOBT: 1

  • Collect two samples from each of three consecutive bowel movements
  • Samples should be examined without rehydration
  • Dietary restrictions recommended (avoid red meat, vitamin C, NSAIDs)

• For FIT: 1

  • Collect samples according to manufacturer's instructions
  • No dietary restrictions required
  • Test performed at home by the patient

Testing Frequency

• Annual testing is recommended for both gFOBT and FIT 1
• Annual testing is more effective than biennial testing 1

Follow-up of Positive Results

• Any positive result requires follow-up with colonoscopy 1
• Colonoscopy should examine the entire colon 1
• Follow-up should be performed in a timely manner 1

Effectiveness and Performance Characteristics

• Mortality Reduction:

  • gFOBT has demonstrated colorectal cancer mortality reduction of 15-33% in randomized controlled trials 1
  • Annual testing with high-sensitivity gFOBT reduced mortality by 33% after 13 years 1
  • Biennial testing reduced mortality by 15-21% 1

• Test Performance:

  • Sensitivity of single gFOBT is low (30-50%), but repeated annual testing can detect up to 92% of cancers 1
  • FIT has superior sensitivity compared to gFOBT 1
  • Both tests have lower sensitivity for adenoma detection than for cancer detection 2

Common Pitfalls and Limitations

• False Positives and Negatives:

  • Most people with positive tests will not have colorectal neoplasia (false positives) 1
  • Single-test sensitivity is limited, requiring regular repeated testing 1
  • Interval cancers (developing between screening periods) remain a concern 2

• Patient Adherence:

  • Effectiveness depends on patient compliance with regular testing 1
  • If patients are not willing to undergo repeated testing or follow-up colonoscopy for positive results, these programs will not be effective 1

• Test Interpretation:

  • Rehydration of gFOBT slides is not recommended as it increases false positive rates 1
  • Digital rectal exam with single stool sample testing is not an adequate screening strategy 1

Alternative Screening Options

For patients who prefer alternatives to fecal blood testing, other recommended screening options include:

• Colonoscopy every 10 years 1
• Flexible sigmoidoscopy every 5 years 1
• CT colonography every 5 years 1
• Multi-targeted stool DNA test (FIT-DNA) every 1-3 years 1

Special Considerations

• Age Considerations:

  • Recent guidelines have lowered the recommended starting age to 45 years for average-risk individuals 1
  • Screening may have diminishing returns after age 75, especially for those previously screened 1

• Risk Stratification:

  • Patients with family history, personal history of adenomatous polyps, inflammatory bowel disease, or genetic syndromes require different screening protocols 1

• Test Selection:

  • FIT generally has better performance characteristics than gFOBT 1
  • Patient preference and adherence should be considered when selecting a screening method 1