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Occult Blood

Source Stool
Mnemonic OBH1, OBH2, OBH3 if three cards received
OBHR if one card received

CLS staff:
- If a community patient or an outpatient arrives in the lab with a requisition for Occult Blood, refer to Fecal Immunochemical Test regardless of patient's age.
- If a collected occult blood card is received in the lab, order with appropriate Occult Blood mnemonic and send for testing.
Specimen Requirements Random stool collection.

Forward stool specimen in a closed container or on an Occult Blood card.

Stool Test Collection Instructions - form # CH3007
Specimen Handling
Additional Information

Guaiac occult blood remains the test of choice for acute, non-screening purposes.

Test limitations:
The physician should determine on an individual patient basis, the need for asking their patients to temporarily implement medication and dietary restrictions.  Otherwise, these limitations should be considered when interpreting Fecal Occult Blood Test (FOBT) results.

If a patient has any questions regarding this information, he or she should contact their physician.

The laboratory test for fecal occult blood is guaiac based and detects the peroxidase activity of hemoglobin.  False positive FOBT can occur in patients using the following medications for ≤ 7 days before and during collection, e.g. aspirin (> 325 mg/day), non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen (Advil ®, Motrin ®), naproxen and anticoagulants. Patients on peroxidase-enriched diets for 3 days before and during collection can have false positive FOBT, e.g. red meat (beef, lamb or liver), melons, cantaloupe, cauliflower, radishes, broccoli, cucumbers, horseradish, parsnips, citrus fruits and juices.  False negative FOBT can occur in patients using Vitamin C (> 250 mg/day) for 3 days before and during collection.

The Hemoccult test is only validated for use with stool specimens. Testing will not be performed on alternate specimens.

Physician Information

Testing Location Chemistry-ACH, FMC, PLC, RGH, SHC & Hematology-DSC
Rural: DDHS, HRH, SDHS
Testing Frequency Daily
Alternate Name(s) Fecal Occult Blood, Guaiac FOBT, Stool Occult Blood
Reference Interval Negative