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.
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 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.
A negative test result means that there is no blood in the stool.
What abnormal results mean:
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:
- Nose bleed
- Coughing up blood
Abnormal tests require follow-up with your doctor.
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.