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Stool occult blood test

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  • 1. Fecal occult blood test
    • A fecal occult blood test (FOBT) is a noninvasive test (nothing enters the body). This test detects hidden (occult) blood in the stool. Such blood may come from anywhere along the digestive tract. Hidden blood in stool is often the first, and in many cases the only, warning sign that a person has colorectal disease, including colon cancer .
    • Fecal occult blood is a term for blood present in the feces that is not visibly apparent.
  • 2. How the Test is Performed    
    • There are two types of FOBTs: 1) the traditional guaiac smear test (Hemoccult, Seracult, Coloscreen), and 2) the newer, flushable reagent pads (EZ DetectT, ColoCARE). They are both useful in detecting hidden blood in the stool, and are mainly used for colorectal cancer screening.
    • The tests differ in the way they are performed. The flushable reagent pads are available without a prescription at many drugstores. In contrast, the traditional guaiac smear test is completed and interpreted by a medical professional, and these tests are usually available from a laboratory or a doctor's office.
  • 3.
    • Many consumers prefer the flushable reagent pads because there is no stool handling and no laboratory processing. However, health care providers usually favor the guaiac tests because the large studies that have shown the benefits of colon cancer screening were done with guaiac tests.
  • 4. Why the Test is Performed    
    • This test is mainly performed for colorectal cancer screening. It may also be performed in the evaluation of anemia .
    • Advantages:
    • Noninvasive
    • Low cost
  • 5.
    • Disadvantages:
    • Detects blood in stool, but not its cause.
    • False-positive results are common with some testing methods. This may cause unneeded anxiety about cancer and lead to unnecessary further tests.
    • False-negative results are also common and may miss disease in its early stages.
  • 6. What Abnormal Results Mean    
    • Positive test results may indicate the following:
    • Bleeding esophageal varices
    • Colon polyp or colon cancer
    • Esophagitis
    • Gastritis
    • GI (gastrointestinal) trauma
    • GI tumor
    • Hemorrhoids
  • 7.
    • Fissures (cracks around the anus)
    • Inflammatory bowel disease
    • Peptic ulcer
    • Complications of recent GI surgery
    • Angiodysplasia of the colon
    • Additional conditions under which the test may be performed include the following:
    • Colon cancer screening
    • Evaluation of anemia
  • 8. Risks    
    • A negative test does not necessarily mean there are no colorectal diseases present. Not all polyps bleed, and not all polyps bleed all the time. That is why a FOBT must be used with one of the other more invasive screening measures (sigmoidoscopy, colonoscopy, double barium contrast enema).
  • 9. Considerations    
    • Colonoscopy is generally recommended as the preferred follow-up test to a positive FOBT.
    • Factors that can cause this test to be less accurate include the following:
    • Bleeding gums following a dental procedure
    • Eating red meat within 3 days of the test
    • Eating turnips or horseradish
  • 10.
    • Drugs that can cause GI bleeding include anticoagulants, aspirin, colchicine, iron supplements in large doses, NSAIDs (anti-inflammatory analgesics), and corticosteroids.
    • Drugs that can cause false positive measurements include colchicine, iron, oxidizing drugs (for example, iodine, bromides, and boric acid), and reserpine.
    • Large amounts of vitamin C can cause false-negative results on most FOBTs.
    • In general, avoiding food is not recommended, with the exception of red meat as described above.
  • 11. How the Test is Performed    
    • If the test is performed in an office or hospital, stool may be collected by a doctor during an examination.
    • If the test is performed at home, 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, follow the manufacturer's instructions on how to collect the stool.
  • 12.
    • 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 take stool samples from the toilet bowl water, because this can cause errors.
  • 13.
    • For infants and young children wearing diapers, you can line the diaper with plastic wrap. The plastic wrap is positioned so that it keeps the stool from any urine. Mixing of urine and stool can spoil a good sample.
    • Laboratory procedures may vary. In one type of test, a small sample of stool is placed on a paper card. A drop or two of testing solution is put on the opposite side of the card. A color change indicates the presence of blood in the stool .
  • 14.
    • “ occult” meaning hidden.
    • Purpose: to detect pathological lesions (ex. Carcinoma) before they produce symptoms and while the condition is still amenable to treatment.
    • This testing is widely used in mass screening programs for colorectal cancer.
    • A number of easy-to-use test kits for detection of occult blood are available. Prior to such kits, the traditional method was to expose the sample to a sequence of solutions that included glacial acetic acid, gum guaiac solution and hydrogen peroxide. A blue color indicated a positive test result. The test kits use these same principles, with some using paper impregnated with guaiac. For these reasons, analysis of feces for occult blood is sometimes still referred to as “stool for guaiac.”
  • 15.
    • One of the main problems of testing stools for occult blood is the number of false-positive results that occur.
    • -diet in meat
    • -diets high in certain vegetables (ex. horseradish, and turnips) and in bananas.
    • -bleeding from the gums or nasal passages
    • -therapy with many drugs due to direct and indirect drug effects on the gastrointestinal tract.
    • Includes:
    • --aspirin (300mg/day)
    • --iron preparations
    • --anticoagulant
    • --adrenocorticosteroids
    • --colchicine
    • --phenylbutazone
    • --ascorbic acid (negative)
  • 16.
    • Black stools-associated with upper G.I. bleeding when the hemoglobin has come in contact with gastric acid and has been converted to hematin. (5 days)
    • Red/maroon—liquid consistency – upper G.I. bleeding is massive and the volume increases G.I. motility
    • Bright red – lower G.I. bleeding from hemorrhoids, ulcerative colitis and carcinomas.
  • 17. Occult Blood indications/purposes
    • -known or suspected disorder associated with gastrointestinal bleeding
    • -therapy with drugs that may lead to gastrointestinal bleeding ex. Aspirin, anticoagulants
  • 18. Rectum and Anus
    • Hemorrhoids
    • usual age of occurrence: older adults
    • severity: usually mild; blood is bright red
    • other features: maybe painless or symptomatic often associated with constipation.
  • 19. Anorectal fissure
    • any age
    • usually mild; blood is bright red
    • nearly always painful. Crohn’s disease, anal intercourse may predispose
  • 20.
    • In the event of a positive fecal occult blood test, the next step in the workup is a form of visualization of the gastrointestinal tract (ie: endoscopy , colonoscopy , virtual colonoscopy ).
  • 21.
    • There are three methods for measuring blood in feces :
    • (Hemoccult or Instaccult). This method can reduce death from colorectal cancer.
    • Fecal porphyrin quantification (Hemoquant) - high false positive rate.
    • Immunochemical fecal occult blood tests (HemeSelect), (QuickVue iFOB), (FOBGold or Automated SENTiFOB) or (OC Auto 80 - Automated iFOBT) - more specific.
    • Fecal DNA test (PreGen-Plus) is more sensitive than fecal occult blood in one study (51.6% vs. 12.9%)
  • 22. One method
    • the test involves smearing some feces onto some absorbent paper that has been treated with a chemical. Hydrogen peroxide is dropped onto the paper; if trace amounts of blood are present, the paper will change color. This method works as hemoglobin has a peroxidase -like effect, rapidly breaking down hydrogen peroxide.
  • 23. Fecal Immunochemical Tests
    • These tests detect the globin in feces rather than heme . By detecting globin the tests are both more sensitive and specific for lower gastrointestinal bleeding
  • 24. Insure
    • is designed to address patient ease of use by using a brush, not a wooden stick, to sample stools while in the toilet bowl. Using these tests there is no direct fecal handling and there is no need for changing diet or medication to perform the test.
  • 25. The Clearview iFOB test
    • requires only one specimen, and because it is specific to human hemoglobin, patients are not required to adhere to strict dietary or medication restrictions. For hospitals and large clinics the OC Automated 80 can perform fecal occult blood detection by immunoassay. This method addresses the dietary issues associated with the guaiac test and has been shown to detect many more early stage cancers and polyps.
  • 26. guaiac-based fecal occult blood test
    • usually picks up a daily blood loss of about 10 ml (about two teaspoonfuls). The sensitivity of a single FOBT has been quoted at 30%, but if 3 tests are done (as is standard), the sensitivity rises to 92%.
    • "Normally, there is only about 0.5 to 1.5 ml of blood a day that escapes blood vessels into the stool each day. There are more sensitive tests than the guaiac such as a heme-porphyrin test or an immunochemical test, but the former test is not used much due to the high false positive rate. The latter test is very sensitive -- it picks up as little as 0.3 ml... It does not detect blood from the stomach and upper small intestine so it is much more specific for bleeding from the colon or lower gastrointestinal tract."
  • 27. PreGen-Plus
    • The stool-based DNA test, was capable of detecting several stages of colorectal cancer, in otherwise healthy adults, and most importantly in its' early stage, the easiest and most effective to treat, stage of colorectal cancer.
  • 28. How the Test is Performed    
    • There is no direct handling of stool with this test. You simply note any changes on a card and then mail the results card to your physician.
    • Urinate if you need to, then flush the toilet before you defecate. After the bowel movement, place the chemically treated tissue pad in the toilet. Watch for a change of color on the test area of the pad (results usually appear within two minutes). Note the results on the card provided, then flush the pad away. Repeat for the next two consecutive bowel movements.
  • 29.
    • Causes for a positive test are:
    • 2-10%: cancer ( colorectal cancer , gastric cancer )
    • 20-30% adenoma or polyps
    • Bleeding peptic ulcer
    • Angiodysplasia of the colon

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