What does a positive Cologard (fecal occult blood test) mean?

What Does a Positive Cologard Test Mean?

A positive Cologard test indicates a high likelihood of colorectal cancer or advanced precancerous lesions and requires prompt follow-up with a diagnostic colonoscopy to examine the entire colon.

Understanding Cologard Testing

Cologard is a multi-target stool DNA (mt-sDNA) test that combines:

• Fecal immunochemical testing (FIT) for blood
• DNA methylation markers (BMP3 and NDRG-4)
• Assessment of KRAS mutations
• A marker of total human DNA

This comprehensive approach gives Cologard superior detection capabilities compared to traditional fecal occult blood tests:

• 92.3% sensitivity for colorectal cancer (vs. 73.8% for FIT alone) 1
• 42.4% sensitivity for advanced precancerous lesions (vs. 23.8% for FIT alone) 1
• 86.6% specificity (lower than FIT's 94.9%) 1

Clinical Significance of a Positive Result

A positive Cologard result requires follow-up for several important reasons:

1. Cancer Detection: The high sensitivity (92.3%) means that a positive result has a strong correlation with the presence of colorectal cancer 1

2. Advanced Adenoma Detection: While less sensitive for precancerous lesions (42.4%), Cologard still detects these important lesions at nearly twice the rate of FIT alone 1

3. Required Follow-up: According to the National Comprehensive Cancer Network (NCCN) guidelines, any positive stool-based test, including Cologard, requires a diagnostic workup with colonoscopy to examine the entire colon 2

Follow-up Protocol

When a Cologard test is positive:

1. Mandatory Colonoscopy: The U.S. Multi-Society Task Force on Colorectal Cancer emphasizes that any positive non-invasive screening test, including Cologard, requires follow-up with colonoscopy 1

2. Timing: The Veterans Health Administration recommends that follow-up colonoscopy should be performed within 60 days of a positive result 1

3. Risk of Delay: Delays beyond 270 days in follow-up colonoscopy are associated with significantly increased risk of colorectal cancer (OR: 1.48) 1

Common Pitfalls to Avoid

1. Ignoring Positive Results: A positive Cologard test should never be dismissed without proper follow-up, even if the patient is asymptomatic

2. Repeating the Test: A positive Cologard should not lead to repeating the stool test; colonoscopy is the required next step 2

3. Assuming False Positive: While Cologard has a lower specificity than FIT (86.6% vs. 94.9%), a positive result should not be dismissed as a false positive without colonoscopy 1

4. Delayed Follow-up: Timely colonoscopy is essential, as delays beyond 270 days significantly increase colorectal cancer risk 1

Special Considerations

1. Patients with History of Polyps: These patients should undergo direct visualization with colonoscopy rather than stool-based testing for subsequent screenings 1

2. Screening Intervals: The NCCN notes that appropriate screening intervals for stool DNA testing cannot be firmly recommended due to limited data 1

3. Upper GI Evaluation: For patients with a positive Cologuard and negative colonoscopy, evaluation of the upper gastrointestinal tract is not routinely indicated 2

By understanding the significance of a positive Cologard test and following appropriate follow-up protocols, clinicians can help ensure that patients receive timely diagnosis and treatment for colorectal cancer and precancerous lesions, ultimately improving outcomes related to morbidity and mortality.