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Introduction ⬇

The most frequently performed fecal analysis is chemical screening for the detection of occult (i.e., hidden) blood. Bleeding in the upper GI tract may produce a black, tarry stool. Bleeding in the lower GI tract may result in an overtly bloody stool. However, no visible signs of intestinal bleeding may be present with smaller amounts of blood found in stool in early stages of GI diseases; thus, the chemical detection of occult blood is necessary to identify and treat disease early in its course. However, occult blood testing is controversial, owing to many false-positive and false-negative results. If the patient preparation and collection of specimen are followed explicitly, the results are more accurate.

An average, healthy person passes up to 2.0 mL of blood per 150 g of stool into the GI tract daily. Passage of more than 2.0 mL of blood in the stool in 24 hours is pathologically significant. Detection of occult blood in the stool is very useful in detecting early disease of the GI tract. This test demonstrates the presence of blood produced by upper GI bleeding, as in the presence of gastric ulcer; it also screens for colonic carcinomas while they are still in the localized stages. With proper medical follow-up, a 92% 5-year relative survival rate has been demonstrated for treatment of stage I colon cancer.

Normal Findings ⬆ ⬇

Negative for blood

Procedure ⬆ ⬇

  1. Collect a random, fresh stool specimen following the procedure for Collection and Transport of Random Specimens. Observe standard precautions. Tests for detecting fecal blood use the pseudoperoxidase activity of hemoglobin reacting with hydrogen peroxide to oxidize a colorless compound to a colored one (usually blue). Hemoccult II (Beckman Coulter) is a widely used commercial test with a low percentage of false-positive results. This test system uses guaiac-impregnated filter paper as the chromogen that produces the blue color in a positive reaction.

  2. Apply a thin smear of stool inside the indicated circle using a wood applicator stick and allow it to dry. If stool is bloody, the collector may be at risk for hepatitis B, hepatitis C, or HIV infection.

  3. Protect the Hemoccult slide from light, heat, and humidity. Do not refrigerate.

  4. Do not allow the delay between smearing the stool and testing to exceed 14 days. Do not refrigerate sample before testing.

Clinical Implications ⬆ ⬇

  1. Stool that appears dark red to tarry black indicates a loss of 50–75 mL of blood from the upper GI tract. Smaller quantities of blood in the GI tract can produce similar-appearing stools or appear as bright red blood.

  2. A stool sample should be considered grossly bloody only after a chemical testing for presence of blood. This will eliminate the possibility that abnormal coloring caused by diet or drugs may be mistaken for bleeding in the GI tract.

  3. Positive test for occult blood may be caused by the following conditions:

    1. Carcinoma of colon

    2. Ulcerative colitis and other inflammatory lesions

    3. Adenoma

    4. Diaphragmatic hernia

    5. Gastric carcinoma

    6. Rectal carcinoma

    7. Peptic ulcer

    8. Gastritis

    9. Vasculitis

    10. Amyloidosis

    11. Kaposi sarcoma (tumors caused by human herpesvirus 8 [HHV8] presenting with cutaneous lesions)

Clinical Alert

  1. To be accurate, the test employed must be repeated 3–6 times on different stool samples; some bowel lesions may bleed intermittently.

  2. The patient’s diet should be free of red/rare meat and fruit and vegetable sources of peroxidase activity (e.g., turnips, parsnips, horseradish, radishes, mushrooms, cauliflower, broccoli, cantaloupe, apples, bananas). Only after following this regimen can a positive series of tests be considered an indication for further patient evaluation and testing.

Interventions ⬆ ⬇

Pretest Patient Care

  1. Explain purpose of test, procedure for stool collection, and interfering factors, as well as the need to follow appropriate stool collection protocols for using a special kit for fecal occult blood or a plastic container with a lid.

  2. Recommend that the patient consume a high-residue diet, starting 72 hours before and continuing throughout the collection period. Roughage in diet can increase test accuracy by helping to uncover silent lesions that bleed intermittently. The diet may include the following:

    1. Meats: only small amounts of chicken, turkey, and tuna

    2. Vegetables: generous amounts of both raw and cooked vegetables, including lettuce, corn, spinach, carrots, and celery; avoid vegetables with high peroxidase activity (see 3b, Interfering Factors)

    3. Fruits: plenty of fruits, especially prunes

    4. Cereals: bran and bran-containing cereals

    5. Moderate amounts of peanuts and popcorn daily. If any of the foods listed earlier are known to cause discomfort, the patient should consult the healthcare provider.

  3. Advise the patient to avoid barium enemas for 72 hours before and during stool specimen collection.

  4. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Procedural Alert

Instruct patients to observe the following procedures:

  • Do not collect samples during or until 3 days after menstrual period or while the patient has bleeding hemorrhoids or blood in the urine.

  • Do not consume the following medications, vitamins, and foods: For 7 days before and during the test period, avoid aspirin or other NSAIDs; for 72 hour before and during the test period, avoid vitamin C in excess of 250 mg/24 hr (250 mg/d) (from all sources, dietary and supplementary), red meat (e.g., beef, lamb), including processed meats and liver, and raw fruits and vegetables (see items listed in 3b, Interfering Factors).

  • Remove toilet bowl cleaners from toilet tank and flush twice before proceeding to defecate.

  • Collect samples from three consecutive bowel movements or three bowel movements closely spaced in time and spread a small stool sample (about 1 mL) on each of the three slides or card provided.

  • Protect card or slides from heat, light, and volatile chemicals (e.g., iodine, bleach). Keep cover flap of slides closed when not in use.

Posttest Patient Care

  1. Have the patient resume a normal diet after testing is complete.

  2. Review occult blood test results; report and record findings. Modify the nursing care plan as needed. Counsel the patient regarding abnormal findings and monitor as necessary. Explain that further testing (e.g., barium enema, defecography) and follow-up may be required.

  3. Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

Clinical Alert

Blood in the stool is abnormal and should be reported and recorded

Interfering Factors ⬆

  1. Drugs such as salicylates (aspirin), steroids, indomethacin, nonsteroidal anti-inflammatory drugs (NSAIDs), anticoagulants, colchicine, and antimetabolites are associated with increased GI blood loss in average, healthy persons and with more pronounced bleeding when disease is present. GI bleeding can also follow parenteral administration of the aforementioned drugs and should be avoided 7 days before testing.

  2. Drugs that may cause false-positive results for occult blood testing include the following:

    1. Boric acid

    2. Bromides

    3. Colchicine

    4. Iodine, povidone-iodine

    5. Other drugs (see Appendix E)

  3. Foods that may cause false-positive results for occult blood testing include the following:

    1. Meats, including processed meats and liver, that contain hemoglobin, myoglobin, and certain enzymes and can give false-positive test results for up to 4 days after consumption

    2. Vegetables and fruits with peroxidase activity (e.g., turnips, parsnips, radishes, horseradish, mushrooms, broccoli, cauliflower, apples, bananas, cantaloupe)

  4. Substances that cause false-negative results for occult blood testing include the following:

    1. Ascorbic acid (vitamin C) in excess of 250 mg/d

    2. Vitamin C–enriched foods and juices

    3. Iron supplements that contain vitamin C in excess of 250 mg

    4. Other drugs (see Appendix E)

  5. Other factors affecting test results include the following:

    1. Bleeding hemorrhoids may produce erroneous results; take samples from center of stool to avoid this error.

    2. Collection of specimen during menstrual period.

    3. Hematuria (i.e., blood in urine).

    4. Some long-distance runners have positive outcomes for occult blood.

    5. Toilet bowl cleansers may interfere with the chemical reaction of the test; remove bowl cleaners and flush twice before proceeding with the test.