Patient care diagnostic tools, tests, procedures
Stool guaiac test
Definition: A test that detects the presence of hidden (occult) blood in the stool. 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 Plus®.
Alternative Names: Guaiac smear test; Fecal occult blood test - guaiac smear; Stool occult blood test - guaiac smear
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 properly, isolating 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 the stool is placed on a special 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.
Discontinue drugs that can interfere with the test such as vitamin C and aspirin if possible.
How the test will feel: This test involves only normal bowel functions, and there is no discomfort, other than the unpleasant task of collecting stool samples.
Why the test is performed: This test is a screening test to detect blood in the gastrointestinal tract.
Normal minute amounts of occult blood that are passed into the gastrointestinal (GI) tract are not enough to be picked up by the standard tests such as the guaiac test.
Normal Values: A "negative" test result is normal.
Abnormal results may indicate:
- Use of aspirin or NSAIDS (e.g., Ibuprofen)
- Colon polyp
- Colon cancer
- GI (gastrointestinal) trauma
- Other benign or malignant GI tumors besides colon cancer or colon polyps
- Inflammatory bowel disease
- Peptic ulcer
- Recent GI surgery
- 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
What the risks are: There can be false-positives and false-negatives. Using proper stool collection technique, avoiding certain drugs that may interfere with the test and observing the dietary restrictions indicated above can minimize these measurement errors.