Fecal occult blood test (FOBT / FIT)

What it measures

Detects hidden blood in stool. The immunochemical test (FIT) detects human hemoglobin and is preferred for colorectal cancer screening; guaiac tests detect peroxidase activity.

Specimen and preparation

• Specimen: Stool
• Tube: Stool top
• Preparation: Guaiac test: avoid red meat, vitamin C and NSAIDs for 3 days. FIT: no diet restriction.

Reference range

Reference ranges differ between laboratories, methods and populations. Always use the range printed on your own lab report.

Causes of high values

• Colorectal cancer or adenomatous polyps
• Peptic ulcer or upper GI bleeding (guaiac more than FIT)
• Inflammatory bowel disease
• Hemorrhoids, angiodysplasia

Method

Immunochemical (FIT) or guaiac-based

Good to know

A positive screen needs colonoscopy; a negative result does not rule out cancer.

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