Lesson 1, Topic 1
In Progress

Stool-Based Tests

April 11, 2024

Learning Objective: Examine stool-based tests.
There are two main types of stool tests:
            • Fecal occult blood test (FOBT): Detects blood in the stool specimen
            • Stool DNA test: Detects genetic material from polyps and cancerous tumors in the stool specimen
The following sections describe these tests.

Fecal Occult Blood Tests
Learning Objective: Describe fecal occult blood tests.
      The fecal occult blood test (FOBT) checks a sample of stool for occult blood. Blood in the stools can be caused by hemorrhoids, diverticulosis, ulcers, colitis, and polyps. There are two main types of FOBT: the guaiac fecal occult blood test (gFOBT) and the fecal immunochemical test (FIT).

Guaiac Fecal Occult Blood Test
      The guaiac fecal occult blood test is a stool test that looks for the presence of occult blood. This is a common test in the ambulatory care environment. The medical assistant needs to coach the patient on both the preparations for the gFOBT and how to collect the stool specimens (Procedure 35.6). Usually, the patient is asked to collect samples from two or three stools on consecutive days. Each hemoccult test card has two locations (A and B) for samples. One card should be used on each day.
      When the hemoccult test cards are returned to the lab, the company recommends that the test be developed no sooner than 3 days after the stool sample was applied. If immediate testing is required, wait 3 to 5 minutes for the sample to penetrate the test paper. Open the back of the slide and apply 2 drops of the hemoccult developer to the guaiac paper over each smear (Procedure 35.7). The medical assistant should read the results within 60 seconds. Any trace of blue on the specimen smear or near the edge is considered a positive test result for occult blood (FIGURE 35.15). The medical assistant must also apply 1 drop of the developer between the positive and negative Performance Monitors areas, for quality control. The results must be read within 10 seconds. The hemoccult card and the developer are functioning if a blue color appears in the positive Performance area and no blue appears in the negative Performance Monitors area.

Fecal Immunochemical Test
The fecal immunochemical test (FIT), also called the immunochemical fecal occult blood test (iFOBT), is a screening test for colon cancer. It only detects human hemoglobin from the large intestine (e.g., cecum, colon, or rectum). Hemoglobin from bleeding occurring from the mouth to the small intestine is generally degraded by the digestive and enzyme processes. Food and medications do not affect this test, so it tends to have fewer false-positive results than the gFOBT.

FIGURE 35.15  Negative and positive hemoccult results. From Roberts J, Hedges J: Clinical procedures in emergency medicine, ed 5, Philadelphia, 2010, Saunders.

InSure ONE
InSure ONE is a FIT that detects human hemoglobin in samples of toilet bowel water collected around the feces. The toilet bowl water is collected after the person brushes the surface of the feces to release any blood into the water. The patient is given the test to take home, along with the following instructions:
            1. Do not collect samples 3 days before, or during, or 3 days after the menstrual period; if the patient has bleeding hemorrhoids; or if there is visible blood in the urine.
            2. Store the collection kit at room temperature away from heat and direct sunlight.
            3. There are no preparations for the test.
            4. Label the card as indicated.
            5. Flush the toilet before starting. After having the bowel movement, put the used toilet paper in the wastebasket instead of the toilet.
            6. Follow the kit instructions:
                      a. Use the brush from the kit to brush the surface of the feces/stool for about 5 seconds.
                      b. Then dip the brush into the toilet water before touching the brush to the space indicated on the test card.
            c. Wrap the brush in toilet paper and discard it in the wastebasket.
            7. Seal the test card and return as directed to your provider or the laboratory.

Multitargeted Stool DNA Test
Learning Objective: Describe the multitargeted stool DNA test.
      The multitargeted stool DNA test (MT-sDNA) detects abnormal DNA, along with the presence of occult hemoglobin in the stool. An example of a multitargeted stool DNA test (MT-sDNA) is the Cologuard, which tests stool for cancer and precancerous cells. Cologuard screens for DNA markers and the presence of occult hemoglobin in stool (Procedure 35.8). The patient is asked to obtain the sample at home and mail the test to the laboratory.
      The patient is given the test to take at home, along with the following directions:
                      1. Do not obtain the sample if you have diarrhea or obvious blood in the urine or stool (e.g., bleeding hemorrhoids, bleeding wounds on the hands, or menstruation).
                      2. There is no preparation required for this test.

FIGURE 35.16  Cologuard Kit.Clockwise from upper left corner: shipping box, sample (specimen) container, bottle of preservative, patient direction booklet, shipping and specimen labels, tube, and bracket.

FIGURE 35.17  Probe and tube from the Cologuard kit.

            3. Store the kit at room temperature, away from heat, direct sunlight, children, and pets.
            4. The kit contains a bracket, sample container, tube with a probe, bottle of preservative, shipping label, and specimen labels (FIGURE 35.16).
            5. The bracket is placed in the toilet. The lid is removed from the stool sample container, and the container is placed into the bracket.
            6. When having the bowel movement, the person must avoid getting toilet paper and urine in the stool sample container.
            7. Following the test directions, the person must scrape the stool sample with the probe to get a small sample (FIGURE 35.17). In addition, the preservative must be poured onto the stool in the stool sample container.
            8. Both samples (sample probe tube and sample container) must be sealed tightly, labeled, packed in the special shipping box, and mailed to the lab within a day. The lab must get the sample within 3 days.