NHA Certified Clinical Medical Assistant (CCMA)Clinical Patient CareHard
A medical assistant is preparing to perform a fecal occult blood test (FOBT) using a guaiac card. The patient reports consuming a large amount of red meat yesterday. Which of the following instructions should the medical assistant give the patient?
- ACollect the sample today and note the dietary intake on the lab requisition.
- BTake an antacid before collecting the sample to counteract dietary effects.
- CReschedule the test for a later date to ensure accurate results.
- DProceed with the test, as diet does not affect FOBT results.
Show answer & explanationAnswer & explanation
Correct answer: C. Reschedule the test for a later date to ensure accurate results.
A guaiac-based FOBT detects peroxidase activity, which is present in red meat. Consuming red meat within 3 days prior to the test can lead to a false-positive result, indicating blood when none is present. Therefore, rescheduling the test after a period of dietary restriction is necessary for accurate results.
Why the other options are wrong
- A. While noting dietary intake is good practice, it does not prevent a false-positive result, which can cause unnecessary anxiety and further invasive testing.
- B. Antacids do not prevent false positives from red meat consumption in a guaiac FOBT.
- D. Diet, especially red meat, significantly affects guaiac FOBT results, leading to false positives.
FOBT Interference (Guaiac)
Guaiac-based Fecal Occult Blood Tests (FOBT) can be affected by dietary intake and certain medications. Red meat and some vegetables contain peroxidase, leading to false-positive results, while Vitamin C can cause false negatives.
- Red meat causes false positives (peroxidase).
- Vitamin C causes false negatives.
- Patient prep is crucial for accuracy.
Memory trick: No red meat, no false bleed, for an accurate test, take heed.