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Stool Guaiac

Definition

The stool guaiac test finds hidden (occult) blood in the stool (bowel movement). It is the most common form of fecal occult blood test (FOBT) in use today.

Alternative Names

Guaiac smear test; Fecal occult blood test - guaiac smear; Stool occult blood test - guaiac smear

How the test is performed

If the test is performed in an office or hospital, stool may be collected by a doctor during an examination.

If the test is performed at home, a stool sample from three consecutive bowel movements is collected, smeared on a card, and mailed to a laboratory for processing. In order to ensure the accuracy of the guaiac test, follow the manufacturer's instructions on how to collect the stool.

There are many ways to collect the samples. You can catch the stool on plastic wrap that is loosely placed over the toilet bowl and held in place by the toilet seat. Then put the sample in a clean container. One test kit supplies a special toilet tissue that you use to collect the sample, then put the sample in a clean container. Do not take stool samples from the toilet bowl water, because this can cause errors.

For infants and young children wearing diapers, you can line the diaper with plastic wrap. The plastic wrap is positioned so that it keeps the stool away from any urine. Mixing of urine and stool can spoil the sample.

Laboratory procedures may vary. In one type of test, a small sample of stool is placed on a paper card and a drop or two of testing solution is added. A color change indicates the presence of blood in the stool.

How to prepare for the test

Do not eat red meat, any blood-containing food, cantaloupe, uncooked broccoli, turnip, radish, or horseradish for 3 days prior to the test.

You may need to stop taking medicines that can interfere with the test. These include vitamin C and nonsteroidal anti-inflammatory medicines such as ibuprofen and aspirin. Check with your health care provider regarding medication changes that may be necessary. Never stop or decrease any medication without consulting your health care provider.

How the test will feel

There is no discomfort when the test is done at home, because this test only involves normal bowel functions. If stool is collected during an exam, there may be some discomfort in the anal canal and rectum.

Why the test is performed

This test is a screening test to detect blood in the digestive tract.

Normal Values

A negative test result means that there is no blood in the stool.

What abnormal results mean

Abnormal results may indicate:

  • Angiodysplasia of the GI tract
  • Colon cancer or other gastrointestinal (GI) tumors
  • Colon polyps
  • Esophageal varices and portal hypertensive gastropathy
  • Esophagitis
  • Gastritis
  • GI infections
  • GI trauma or bleeding from recent GI surgery
  • Hemorrhoids
  • Inflammatory bowel disease
  • Peptic ulcer

Stool guaiac testing is sometimes used to screen for colon cancer, but it is not a reliable test for this purpose, and other screening methods should be used.

Additional non-GI-related causes of positive guaiac test may include:

  • Nose bleed
  • Coughing up blood

Abnormal tests require follow-up with your doctor. In many cases, however, no explanation for the abnormal result is found.

What the risks are

There can be false-positive and false-negative results. Using the right collection technique, avoiding certain drugs, and observing food restrictions can reduce errors.

References

Feldman M, Friedman LS, Brandt LJ, eds. Sleisenger and Fordtran's Gastrointestinal and Liver Disease. 8th ed. Philadelphia, Pa: Saunders Elsevier; 2006:chap 13.

Review Date: 12/7/2009

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Information developed by A.D.A.M., Inc. regarding tests and test results may not directly correspond with information provided by UCSF Medical Center. Please discuss with your doctor any questions or concerns you may have.