Cologuard (Multi-target Stool DNA) — Colorectal Cancer

Test Characteristics

Metric	Value
False-negative rate	7% (sensitivity 93%)
False-positive rate	16% (specificity 84%)
Bayes factor (positive test)	5×
Bayes factor (negative test)	1/10×
Base rate	0.5% for CRC in average-risk adults

Interpreting Results

Scenario	Prior	+ Result	− Result
Average-risk adult	0.5%	5 × 0.5% = 2.5%0.5%× 52.5%	1/10 × 0.5% = 0.05%0.5%÷ 100.05%

Weaker positive Bayes factor than FIT due to higher false-positive rate, but stronger negative Bayes factor because it misses fewer cancers. Positive result warrants follow-up colonoscopy.

• + result: risk goes from identical twin (0.5%) to near red hair (2.5%)
• − result: risk drops to near fatal car crash (0.05%)

Sources:

• USPSTF systematic review, 2021. sDNA-FIT combination test.