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Fecal occult blood Medical Background

	Overview Medical Background Literature

Medical Background

Source & biological action

Occult gastrointestinal bleeding typically refers to bleeding that is not apparent to the patient. Normally, approx. 0.5 - 1.5 ml blood is lost from the gastrointestinal tract per day. This amount is typically not detected by occult blood tests. Occult blood in stool is one of the initial symptoms of intestinal cancer. However, many gastrointestinal lesions can bleed and cause a positive fecal occult blood test.

Differential diagnosis of occult gastrointestinal bleeding

Mass lesions	Carcinoma (any site) Large (> 1.5 cm) adenoma (any site)
Inflammation	Erosive esophagitis Erosive gastritis Ulcer Cameron lesions Celiac disease Ulcerative colitis, non-specific colitis Crohn's disease Idiopathic cecal ulcer
Vascular disorders	Vascular ectasia (any site) Portal hypertensive gastropathy or colopathy Watermelon stomach Varices (any site) Hemangioma Dieulafoy's vascular malformation
Infectious diseases	Hookworm, Whipworm Strongyloidiasis Ascariasis Tuberculous enterocolitis Amebiasis
Surreptitious bleeding	Hemoptysis Oropharyngeal bleeding (including epistaxis)
Other causes	Hemosuccus pancreaticus Hemobilia Long-distance running Factitious cause

The most common abnormalities are highlighted bold.

Indications for testing

Testing for occult blood with hemo FEC^® is indicated for screening for intestinal cancer.

Patient preparation

• From 3 days before starting the hemo FEC^® test until the end of the test period, the patients should consume a diet as rich as possible in roughage (vegetables, salad, fruit, whole wheat products). They should avoid raw meat and sausage (salami, tartar sausage, black pudding) because these may produce false-positive results.
• The consumption of vitamin C tablets may affect the test and cause false-negative results (not with small doses of vitamin C in multivitamin preparations). Due to their colour, iron- or bismuth-containing drugs disturb when reading the cards. Enemas or suppositories should not be applied during the days of testing.
• The test should be postponed in the case of diarrhea or menstruation, but does not need to be postponed if slight gum bleeding or epistaxis is present.

Determination

hemo FEC^® is an easy, quick and cost-effective test for the detection of occult blood in stool. It is a qualitative, chromatographic guaiac-based test that does not require handling of feces in the laboratory. The patient applies 2 separate samples of each of 3 successive bowel movements onto 3 test cards. In the practice, 2 drops of developer reagent are applied onto each fecal sample.

Results

Any blue colouration of a hemo FEC^® test card that occurs within 30 seconds is interpreted as a positive result. In screening studies, 2 - 16 % of the patients tested had positive tests (including false-positive tests). The lower detection limit of hemo FEC^® of 2 - 3 ml of blood in 100 g of stool was determined in experimental models by adding blood to homogenized stool.

False-negative test results are mainly caused by only intermittent bleeding or inhomogeneous composition of stool. Furthermore, test results may be false-negative in the case of lesions in the right colon due to bacterial degradation of haemoglobin.

By repeated testing, as required for screening purposes, false-negative results are clearly reduced.

Clinical aspects

Intestinal cancer (colorectal carcinoma) is the second most frequent form of cancer for both sexes. Since intestinal cancer generally develops very slowly, 90 % of intestinal tumours can be cured if detected in an early stage. Fecal occult blood testing should be offered to all persons at average risk, beginning at the age of 40 - 50 years.

Tips & recommendations

• Do not rehydrate the hemo FEC^® test cards, since rehydration markedly raises the sensitivity of the test but reduces its specificity.
• A positive hemo FEC^® test result in one or more cards should lead to a complete colorectal examination which is usually done by colonoscopy. A negative result cannot rule out colorectal cancer. If symptoms that indicate possible colorectal cancer develop after a negative screening result, timely evaluation is warranted.
• Occult blood testing with hemo FEC^® is ideal for routine screening. If there is a family history of colorectal carcinoma or polyps or if inherited syndromes of colorectal cancer are present (e. g., familial adenomatous polyposis or hereditary non-polyposis colorectal cancer) a complete colorectal evaluation is recommended or even mandatory.
• Neither oral anticoagulants nor acetylsalicylic acid per se appear to cause positive guaiac-based fecal occult blood tests.

HEMO FEC is a trademark of a member of the Roche Group.

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