5. Lab- Fecal Occult Blood Test

Patient Instructions & Interferences

  • For accurate test results:

    • Apply samples from bowel movements collected on three different days to the slide.

    • Important Do Not Collect Sample Circumstances:

    • If blood is visible in your stool or urine (e.g., menstruation, active hemorrhoids, urinary tract infection). Contact your doctor in such cases.

    • For most accurate test results:

    • Collect each stool sample before contact with toilet bowl water.

    • Use the collection tissue provided or any other clean, dry container.

    • Return completed slide to your doctor or laboratory no later than 14 days after your first sample collection.

    • Protect slide from heat, light, and volatile chemicals (iodine, ammonia, bleach, and household cleaners).

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

Drug Guidelines

  • For optimal test results, follow these medication restrictions:

    • Avoid for seven days before and during stool collection period:

    • Non-steroidal anti-inflammatory drugs such as ibuprofen, naproxen, or aspirin (more than one adult aspirin a day).

    • Acetaminophen (e.g., Tylenol*) can be taken as needed without restrictions.

    • Avoid for three days before and during the stool collection period:

    • Vitamin C in excess of 250 mg a day from supplements, and citrus fruits and juices to prevent false negatives.

Diet Guidelines

  • For three days before and during stool collection:

    • Avoid red meats (including beef, lamb, and liver).

    • Consume a well-balanced diet rich in fiber including bran cereals, fruits, and vegetables.

Notes

  • Consult your doctor or pharmacist regarding any questions about medications you regularly take.

  • The Recommended Dietary Allowance (RDA) of vitamin C for adults is 60 mg a day.

  • Note that some iron supplements may contain vitamin C exceeding the 250 mg threshold.

  • Exposure to sunlight may cause discoloration of the collection card to light blue, leading to false positive results.

Principle of the Guaiac Test

  • In dried fecal samples, hemoglobin is very stable and is crucial for the test.

  • Chemical Reaction Explanation:

    • In a positive sample, guaiac resin within the reagent paper is oxidized by hydrogen peroxide (H2O2) from the developer solution, resulting in a blue color.

    • For the oxidation to occur, a hemoglobin molecule acts as a catalyst that transfers an oxygen atom from H2O2 to the guaiac molecule, producing a conjugated blue quinone compound.

    • Each hemoglobin molecule can catalyze this reaction indefinitely as long as guaiac molecules and H2O2 are present.

  • Outcome and Migration of Color:

    • The blue color can only form in the presence of hemoglobin, but it can migrate with the developer solution, appearing as streaks outside the initial sample area.

    • The positive Performance Monitors areas contain a hemoglobin-derived catalyst indicating a blue color will appear 10 seconds after developer application. The negative area contains no catalyst.

Procedure

Collection

  1. Preparing the Slide:

    • Remove the slide from the paper dispensing envelope. Write your name, age, and address on the front of the slide using a ball-point pen. Note: Do not tear the sections apart.

  2. Sample Collection Procedure:

    • Fill in the sample collection date on section 1 before a bowel movement.

    • Flush the toilet and allow it to refill.

    • Unfold the flushable collection tissue and float it on the surface of the water. Edges should stick to the sides of the bowl. Let stool fall onto the collection tissue without contacting the toilet bowl water.

    • Alternative Collection Method: A clean, dry container can also be used to collect the sample.

  3. Smear Application:

    • Open the front of section 1. Use one stick to collect a small sample and apply a thin smear covering Box A.

    • Collect a second sample from a different part of the stool with the same stick and apply a thin smear covering Box B.

    • If tissue was used, flush it; dispose of the stick in a waste container. DO NOT FLUSH STICK.

  4. Secure the Sample:

    • Close and secure the front flap of section 1 by inserting it under the tab. Store the slide in the paper envelope until the next day allowing the sample to dry. Important: Do not place the sampled slide in moisture-proof material such as plastic bags or store in the refrigerator at any time.

  5. Repeat for Additional Samples:

    • Repeat steps 2-4 for the next two days, utilizing sections 2 and 3.

    • Store the final slide in the paper envelope overnight for drying; the next day, remove the slide, place in the Mailing Pouch, seal, and promptly return to your doctor or laboratory.

Developing the Test

  1. Drying Samples:

    • Allow fecal samples to dry for 48-72 hours or more before developing the test to avoid false-positive results that may arise from undigested plant peroxidases.

  2. Applying Developer Solution:

    • Open the back of the slide and apply two drops of Hemoccult Developer directly over each smear on the guaiac paper.

  3. Timing Result Reading:

    • Read results within 60 seconds. Any blue observed on or at the edge of the smear indicates a positive result.

Develop Performance Monitor (Quality Control) Test

  1. Applying Performance Monitor:

    • Apply one drop of Hemoccult Developer between the (+) and (–) Performance Monitor areas.

  2. Interpreting Results:

    • Interpret within 10 seconds. If the slide and developer function correctly, a blue color should appear in the positive Performance Monitor area with no color appearing in the negative area.

  3. Importance of Color Intensity:

    • The shade of blue or intensity should not be used as a reference for determining positive test results.

Interpretation

  • A positive test will present blue streaks on the pad or a blue coloring surrounding the stool sample area after peroxide reagent addition.

  • Visual representations of outcomes are depicted:

    • Figure 1: Negative stool sample

    • Figure 2: Positive stool sample

Bibliography

  • Hemoccult SENSA/Hemoccult II SENSA Product Instructions [PDF]. Retrieved from https://www.beckmancoulter.com/wsrportal/wsr/diagnostics/clinical-products/rapid-diagnostics/hemoccult/index.htm#2/10//0/25/1/0/asc/2/60151///0/1//0//wsrportal/wsr/diagnostics/clinical products/rapid-diagnostics/hemoccult/index.htm/

  • Interpretation of Hemoccult [PDF]. Retrieved from http://www.beckmancoulter.de/beckman2_media/Klinische Diagnostik/Instrumente/PCD/Hemoccult Produkte/Broschüren/34 _ Interpreting Hemoccult _ english.pdf