CLIA Complexity: Waived
Method:
Hemoccult Fecal Occult Blood Test
Principle:
Hemocult is a screening procedure for fecal blood and consists of a cardboard slide with guaiac-impregnated paper in a cardboard frame which permits sample application to one side with development and interpretation on the reverse side. Test is based on the oxidation of phenolic compounds present in the guaiac to quinones resulting in production of the blue color. When a fecal specimen containing occult blood is applied to the test paper, contact is made between hemoglobin and the guaiac. A pseduoperoxidase reaction will occur upon the addition of the developer solution, with a blue chromagen formed proportional to the concentration of hemoglobins. The color reaction will occur after 30 seconds.
Materials:
Hemoccult Slide(s) CAUTION: Protect from heat, sunlight, humidity, fluorescent light, U.V. radiation, excessive air flow or volatile chemicals; store at 15 – 30°C Do not refrigerate or freeze.
Wooden applicator sticks
Hemoccult Fecal Occult Blood Developer <6% Hydrogen Peroxide and Denatured Alcohol WARNING: FLAMMABLE. VAPOR HARMFUL. AVOID CONTACT WlTH EYES OR SKIN. FOR IN VITRO DIAGNOSTIC USE ONLY. Stool collection container (for home collection) Specimen: A thin smear of stool is applied to impregnated filter paper (Sure-Vue slide) using a wooden applicator stick. Specimens are usually collected in groups of three on consecutive days. A clinician may also collect a specimen in a patient examination. (See following special patient instructions for home collection.) Procedure: Hemoccult slides may be collected several ways: a.) The slides may be given to the patient with the following instruction sheet for home collection (see occult blood instruction for patients). b.) The patient may collect the specimen in the lab, and the Clinical Laboratory Scientist will apply a thin smear of stool specimen to the filter paper test areas on the Hemoccult slide(s) using wooden applicator sticks. c.) The clinician may collect a specimen rectally and apply it to the slide. When the labeled slide(s) are returned to the laboratory, open slide cover labeled “Open Tab” If the specimen is thick and/or has been received after more than a week after collection, rehydrating the specimen using 2-3 drops of saline may enhance the sensitivity of the test. Open perforated section on back labeled “FOR LABORATORY USE ONLY.” Apply two drops of developing solution to sample “A” (right side). Read results after 30 seconds: a) A trace of blue is positive for occult blood. b) No indication of blue is negative for occult blood. Repeat step 4 for sample “B” (left side). For Quality Control, apply one drop of developing solution to each control spot (positive and negative red rectangles at bottom of slide). Read results after 30 seconds and within 2 minutes. Enter both patient and QC results as well as Hemoccult Lot#/Exp date in the appropriate fields in the LIS. Quality Control: Positive and negative controls are present on each slide (located in red rectangle) with patient test areas “A” and “B” Negative control must show no trace of blue color. The positive control must produce a blue or blue-green color. lf expected results are not obtained, the slides should be discarded and patient testing repeated using a new slide. Controls are performed with each slide and are recorded along with the patient results in the LIS. Testing two samples of the patient specimen serves as a procedural control for quality assurance since this is a CLIA- waived procedure, and commercial controls are not required. There are three unknown occult blood specimens annually included with the laboratory’s Proficiency testing for additional quality assurance. Limitations: It is important that the slides be read 30 seconds after developer has been added and within 2 minutes. Results obtained with this test cannot be considered conclusive evidence of the presence or absence of gastrointestinal bleeding or pathology. False negative tests may be obtained since most bleeding occurs intermittently. Fecal occult blood tests are designed as a preliminary screen and are not intended to replace other diagnostic procedures. This method will detect only hemoglobin released upon hemolysis of the red cell. Should whole blood be applied to the test paper, it is necessary to hemolyze the red cells by the addition of a drop of water before adding the developer. Expected Results: The guaiac paper tests detect occult blood, but they are not diagnostic for disease. False positive results may result from interfering substances (see chart below) or from, diverticulitis, hemorrhoids, or colitis. Positive tests should be followed by a thorough diagnostic workup. This test will detect 10 mg of hemoglobin per gram of fecal material. Clinical studies demonstrate that the guaiac impregnated slide tests yield a positive result 3-5% in screening programs. The false positive rate was between 1-2% during controlled diet situations that were medically supervised. Interfering Substances: Substance Source Comments Ascorbic acid Vitamin C in high doses (> 250 mg / day) False negative result:
discontinue intake for 2 days prior and during the test period
Peroxidase Fruits and vegetables, such
as turnips, broccoli,
horseradish, cauliflower,
cantaloupe, parsnips and red
radishes False positive result: avoid these
foods 2 days prior to and
continuing through the test
period
Oral medications Aspirin, indomethacin,
reserpine, phenylbutazone,
corticosteroids May cause bleeding or irritation
of the gastrointestinal tract and
should be discontinued for 7
days prior to and during the test period
Heavy alcohol
consumption Alcoholic drinks May cause bleeding or irritation
Of the gastrointestinal tract and
should be discontinued for 7
days prior to and during the test
period
Red meat — May cause false positives:
eliminate red meat from the diet
during the test period
Key Points:
References:
Product Insert, Hemoccult, Beckman Coulter Inc., Brea, CA Sept 2009
