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Alternative NamesGuaiac smear test; Fecal occult blood test - guaiac smear; Stool occult blood test - guaiac smear
Definition Return to top
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.
How the Test is Performed Return to top
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 Return to top
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 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 Return to top
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 Return to top
This test is a screening test to detect blood in the digestive tract.
Normal Results Return to top
A negative test result means that there is no blood in the stool.
What Abnormal Results Mean Return to top
Abnormal results may indicate:
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:
Abnormal tests require follow-up with your doctor.
Risks Return to top
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 Return to topFeldman M, Friedman LS, Brandt LJ, eds. Sleisenger and Fordtran's Gastrointestinal and Liver Disease. 8th ed. Philadelphia, Pa: Saunders Elsevier; 2006:chap 13. Update Date: 3/8/2008 Updated by: Christian Stone, MD, Division of Gastroenterology, Washington University in St. Louis School of Medicine, St. Louis, MO. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.