Fecal Occult Blood

Traces of blood in stool that are too small to see.

Fecal occult blood is blood in the stool in amounts too small to be visible. Detecting it is one of the most established ways to catch colon problems early — which is exactly when they’re most treatable. It’s the marker behind screening programs used worldwide, and the one our Colonox FIT reads at home.

What it is

“Occult” simply means hidden. Small amounts of blood can enter the digestive tract without changing how stool looks, so a chemical test is the only way to know it’s there. A fecal immunochemical test (FIT) detects human hemoglobin specifically, which makes it more accurate than older stool tests — and it doesn’t require any diet changes beforehand.

Why it matters

Polyps and early colorectal cancers often bleed a little, long before they cause symptoms. That’s what makes this marker so valuable: it can surface a problem years before you’d otherwise notice anything. Less serious causes — hemorrhoids, small fissures, inflammation — can also produce hidden blood.

What a result can tell you

A negative result is reassuring, and regular repeat screening keeps it meaningful. A positive result doesn’t mean cancer — most positives turn out to be something less serious — but it does mean the next step is a conversation with your doctor, who will usually recommend a colonoscopy to find the source.

What it can’t tell you

The test can’t tell where blood is coming from or why. A single negative result also doesn’t rule out a problem, which is why screening works on a schedule, not as a one-off. If you have symptoms — visible blood, persistent changes in bowel habits, unexplained weight loss — see a healthcare provider regardless of any test result.