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Stool guaiac (Blood)

A stool guaiac test is a laboratory test that is used to detect the presence of blood in the stool. It is a simple test that involves collecting a small sample of stool and applying it to a special paper or card that contains a chemical called guaiac. If the chemical reacts with the blood in the stool, it will turn a certain color, indicating the presence of blood. Stool guaiac tests are often used to diagnose conditions such as inflammatory bowel disease (IBD), colorectal cancer, and other digestive disorders that can cause bleeding in the intestinal tract. The test is typically performed in a doctor’s office, one of our walk-in urgent care, or a laboratory, and the results are usually available within a few days. The Stool Guiaic test is the most common type of fecal occult blood test (FOBT).

The fecal occult blood

(FOBT) is a laboratory test used to detect the presence of blood in the stool, which may be an indication of polyps or colorectal cancer. It is performed using a kit that can be used at home and involves collecting a small sample of stool and applying it to a special paper or card that contains a chemical called guaiac. If the chemical reacts with the blood in the stool, it will turn a certain color, indicating the presence of blood. It is important to follow the test instructions carefully and avoid certain foods and medications before the test, as they may affect the accuracy of the results. If the FOBT is positive, a colonoscopy will typically be recommended to further investigate the cause of the blood in the stool. The FOBT is generally covered by insurance, including Medicare for individuals over 45.

  • Looks for blood in stool
  • The doctor may ask you to avoid certain foods and medicines
  • No risk involved
  • Inexpensive and generally covered by insurance

Advantages of Stool Guaiac Test

  • Inexpensive; covered by most insurance
  • It can be simple to complete
  • It can be completed in the comfort of your own home

Disadvantages of Stool Guaiac Test

  • Cannot identify polyps; can only detect signs of cancer
  • Will need a colonoscopy if the test is positive
  • Patients may find test unpleasant
  • Requires strict adherence to the test protocol for the test to be accurate (restricted diet and multiple days of stool collection)
  • High false positive rate — non-cancerous conditions may also cause blood in the stool and not specific for human blood
  • May miss tumors that bleed in small amounts or not at all

How the Stool Guaiac Test 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.
  • Be sure to keep the stool away from any urine.
  • Mixing of urine and stool can spoil the sample.

How to Prepare for the Stool Guaiac 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 NSAIDs such as ibuprofen and naproxen. Ask your healthcare provider if you should stop taking these before the test. Never stop or change your medicine without first talking to your provider.

How the Stool Guaiac Test Feel

The at-home test involves a normal bowel movement. There is no discomfort.

You may feel discomfort if the stool is collected during a rectal exam.

Why the Stool Guaiac Test Performed

This test detects blood in the digestive tract. It may be done if:

  • You are being screened or tested for colon cancer.
  • You have abdominal pain, changes in bowel movements, or weight loss.
  • You have anemia (low blood count).
  • 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 on a fecal occult blood test (FOBT) may be due to a variety of conditions that cause bleeding in the stomach or intestinal tract, including:
  • Colon cancer or other gastrointestinal tumors
  • Colon polyps
  • Bleeding veins in the esophagus or stomach (esophageal varices and portal hypertensive gastropathy)
  • Inflammation of the esophagus (esophagitis)
  • Inflammation of the stomach (gastritis) from gastrointestinal infections
  • Hemorrhoids
  • Crohn disease or ulcerative colitis
  • Peptic ulcer

Other causes of a positive test may include:

  • Nosebleed
  • Coughing up blood and then swallowing it

It is important to follow up with a healthcare provider/ Specialist if you receive abnormal results on an FOBT, as further testing may be necessary to determine the cause and guide treatment.

If the stool guaiac test shows evidence of blood in the stool, your doctor will likely order additional tests, including possibly a colonoscopy, to determine the cause of the blood and rule out or confirm a diagnosis of colon cancer. While the stool guaiac test is not designed to diagnose cancer specifically, it can be a useful tool in detecting early signs of the disease. Early detection of colon cancer through screening tests such as colonoscopy can improve the chances of successful treatment.

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.

Alternative Names

Colon cancer – guaiac test; Colorectal cancer –

guaiac test; gFOBT; Guaiac smear test; Fecal occult blood test – guaiac smear;

Stool occult blood test – guaiac smear

Stool Guaiac (Blood)
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