Main Campus: Chesterfield, MO 63017 | 
Stool guaiac test
gFOBT; Guaiac smear test; Fecal occult blood test - guaiac smear; Stool occult blood test - guaiac smear
The stool guaiac test looks for hidden (occult) blood in a stool sample. It can find blood even if you cannot see it yourself. It is the most common type of fecal occult blood test (FOBT).
Guaiac is a substance from a plant that is used to coat the FOBT test cards.
How the Test is Performed
Usually, you collect a small sample of stool at home. Sometimes, a doctor may collect a small amount of stool from you during a rectal examination.
If the test is done at home, you use a test kit. Follow the kit instructions exactly. This ensures accurate results. In brief:
- You collect a stool sample from 3 different bowel movements.
- For each bowel movement, you smear a small amount of the stool on a card provided in the kit.
- You mail the card to a laboratory for testing.
DO NOT take stool samples from the toilet bowl water. This can cause errors.
For infants and young children wearing diapers, you can line the diaper with plastic wrap. Place the plastic wrap so that it keeps the stool away from any urine. Mixing of urine and stool can spoil the sample.
How to Prepare for the Test
Some foods can affect test results. Follow instructions about not eating certain foods before the test. These may include:
- Red meat
- Cantaloupe
- Uncooked broccoli
- Turnip
- Radish
- Horseradish
Some medicines may interfere with the test. These include vitamin C, aspirin, and nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen and naproxen. Ask your health care provider if you need to stop taking these before the test. Never stop or change your medicine without first talking to your provider.
How the Test will Feel
The at-home test involves a normal bowel movement. There is no discomfort.
You may have some discomfort if the stool is collected during a rectal exam.
Why the Test is Performed
This test detects blood in the digestive tract. It may be done if:
-
You are being screened or tested for
colon cancer
Colon cancer
Colon, or colorectal cancer, is cancer that starts in the large intestine (colon) or the rectum (end of the colon). Other types of cancer can affect ...
ImageRead Article Now Book Mark Article - You have abdominal pain, changes in bowel movements, or weight loss
-
You have
anemia
(low blood count)
Anemia
Anemia is a condition in which the body does not have enough healthy red blood cells. Red blood cells provide oxygen to body tissues. Different type...
ImageRead Article Now Book Mark Article - You say you have blood in the stool or black, tarry stools
Normal Results
A negative test result means that there is no blood in the stool.
What Abnormal Results Mean
Abnormal results may be due to problems that cause bleeding in the stomach or intestinal tract, including:
-
Colon cancer or other gastrointestinal (GI)
tumors
Tumors
A tumor is an abnormal growth of body tissue. Tumors can be cancerous (malignant) or noncancerous (benign).
Read Article Now Book Mark Article -
Colon polyps
Colon polyps
A colorectal polyp is a growth on the lining of the colon or rectum.
ImageRead Article Now Book Mark Article -
Bleeding veins in the esophagus or stomach (
esophageal varices
and portal hypertensive gastropathy)
Esophageal varices
The esophagus is the tube that connects your throat to your stomach. Varices are enlarged veins that may be found in the esophagus. These veins may...
ImageRead Article Now Book Mark Article -
Inflammation of the esophagus (
esophagitis
)
Esophagitis
Esophagitis is present when the lining of the esophagus becomes swollen, inflamed, or irritated. The esophagus is the tube that leads from the back ...
ImageRead Article Now Book Mark Article -
Inflammation of the stomach (
gastritis
) from GI infections
Gastritis
Gastritis occurs when the lining of the stomach becomes inflamed or swollen. Gastritis can last for only a short time (acute gastritis). It may als...
ImageRead Article Now Book Mark Article -
Hemorrhoids
Hemorrhoids
Hemorrhoids are swollen veins in the anus or lower part of the rectum.
ImageRead Article Now Book Mark Article -
Crohn disease
or
ulcerative colitis
Crohn disease
Crohn disease is a disease where parts of the digestive tract become inflamed. It most often involves the lower end of the small intestine and the be...
ImageRead Article Now Book Mark ArticleUlcerative colitis
Ulcerative colitis is a condition in which the lining of the large intestine (colon) and rectum become inflamed. It is a form of inflammatory bowel ...
ImageRead Article Now Book Mark Article -
Peptic ulcer
Peptic ulcer
A peptic ulcer is an open sore or raw area in the lining of the stomach or intestine. A gastric ulcer occurs in the stomach. A duodenal ulcer occurs ...
ImageRead Article Now Book Mark Article
Other causes of positive test may include:
- Nosebleed
- Coughing up blood and then swallowing it
If the stool guaiac results come back positive for blood in the stool, your doctor will likely order other tests, usually including a colonoscopy .
Colonoscopy
A colonoscopy is an exam that views the inside of the colon (large intestine) and rectum, using a tool called a colonoscope. The colonoscope has a sm...
The stool guaiac test does not diagnose cancer. Screening tests such as colonoscopy can help detect cancer. The stool guaiac test and other screenings can catch colon cancer early, when it is easier to treat.
Risks
There can be false-positive and false-negative results.
Errors are reduced when you follow instructions during collection and avoid certain foods and medicines.
References
National Comprehensive Cancer Network. NCCN clinical practice guidelines in oncology (NCCN Guidelines): colorectal cancer screening. www.nccn.org/professionals/physician_gls/pdf/colorectal_screening.pdf . Version 1.2015. Accessed February 2, 2016.
Savides TJ, Jensen DM. Gastrointestinal bleeding. In: Feldman M, Friedman LS, Brandt LJ, eds. Sleisenger and Fordtran's Gastrointestinal and Liver Disease . 10th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 20.
US Preventive Services Task Force. Draft recommendation statement: colorectal cancer: screening. October 2015. www.uspreventiveservicestaskforce.org/Page/Document/draft-recommendation-statement38/colorectal-cancer-screening2 . Accessed February 2, 2016.
-
Fecal occult blood test - illustration
A fecal occult blood test is a noninvasive test that detects the presence of hidden blood in the stool. Blood in the stool that is not visible is often the first, and in many cases the only, warning sign that a person has colorectal disease, including colon cancer.
Fecal occult blood test
illustration
-
Fecal occult blood test - illustration
A fecal occult blood test is a noninvasive test that detects the presence of hidden blood in the stool. Blood in the stool that is not visible is often the first, and in many cases the only, warning sign that a person has colorectal disease, including colon cancer.
Fecal occult blood test
illustration
Review Date: 1/28/2016
Reviewed By: Subodh K. Lal, MD, gastroenterologist with Gastrointestinal Specialists of Georgia, Austell, GA. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.
