Stool guaiac test

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


The stool guiac test is a test that detects the presence of hidden (occult) blood in the stool (bowel movement). The stool guaiac is the most common form of fecal occult blood test (FOBT) in use today.

Brand names include Hemoccult, Hemoccult SENSA, ColoScreen, ColoScreen-ES, Seracult, and Seracult Plusreg;.

How the test is performed
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, it is important to follow, whenever available, the manufacturer’s instruction on how to collect the stool.

Adults and children:
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 sample stool specimen from within the toilet bowl water, as this can cause measurement errors.

Infants and young children:
For children wearing diapers, you can line the diaper with plastic wrap. If the plastic wrap is positioned so that it isolates the stool from any urine output, mixing of urine and stool can be prevented for a better sample.

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

How to prepare for the test

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

You may need to discontinue drugs that can interfere with the test such as vitamin C and aspirin if possible. Check with your health care provider regarding medication changes that may be necessary. Never discontinue or decrease any medication without consulting your health care provider.

How the test will feel
Because this test involves normal bowel functions, there is no discomfort.

Why the test is performed
This test is a screening test to detect blood in the gastrointestinal tract.

Normal Values
A negative test result is normal.

What abnormal results mean
Abnormal results may indicate:

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

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

  • Nose bleed  
  • Coughing up blood

Abnormal tests require follow-up with your physician.

What the risks are
There can be false-positive and false-negative results. Using proper stool collection technique, avoiding certain drugs, and observing dietary restrictions can minimize these measurement errors.

Johns Hopkins patient information

Last revised: December 3, 2012
by Levon Ter-Markosyan, D.M.D.

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