Can a patient on Eliquis (apixaban) have a false positive result on a Fecal Occult Blood Test (FOBT) due to gastrointestinal bleeding?

Eliquis (Apixaban) Can Cause False Positive Results on Fecal Occult Blood Tests

Yes, patients on Eliquis (apixaban) can have false positive results on Fecal Occult Blood Tests (FOBT) due to gastrointestinal bleeding caused by the anticoagulant. This is particularly relevant for guaiac-based FOBTs (gFOBT), which detect the presence of blood in stool.

Mechanism and Evidence

Eliquis (apixaban) is an anticoagulant that can increase the risk of bleeding, including gastrointestinal bleeding. According to the FDA drug label, gastrointestinal hemorrhage is listed as a potential adverse reaction in patients taking apixaban 1. This bleeding may be microscopic and not clinically apparent but still detectable by FOBT.

The US Multi-Society Task Force on Colorectal Cancer specifically addresses anticoagulant use in relation to Fecal Immunochemical Tests (FIT), noting that "limited data suggest that intake of aspirin, warfarin, and clopidogrel lower the positive predictive value of conventional gFOBT for advanced neoplasia" 2.

Different Types of FOBT and Their Susceptibility to False Positives

Guaiac-based FOBT (gFOBT)

• More susceptible to false positives from various sources
• Detects the pseudoperoxidase activity of heme or hemoglobin
• Affected by dietary factors and medications 2, 3

Fecal Immunochemical Test (FIT)

• More specific for human blood
• Less affected by medications and dietary factors
• Higher specificity for lower GI bleeding 2, 3

Clinical Implications

1. For Colorectal Cancer Screening:

   • A positive FOBT in a patient on Eliquis requires follow-up with colonoscopy 2
   • The US Multi-Society Task Force states: "There is no rationale to adjust diet or anticoagulation or antiplatelet agents when using FIT-based screening" 2
   • However, this recommendation applies specifically to FIT, not necessarily to guaiac-based tests

2. For Diagnostic Purposes:

   • FOBT is not recommended as a diagnostic test in symptomatic patients 4, 5
   • In emergency settings, FOBT has poor sensitivity and specificity and should not change clinical decision-making 4

Research on Anticoagulants and FOBT

A study specifically examining antithrombotic drugs and immunochemical FOBT found that "the positive predictive value of iFOBT was not affected by ongoing antithrombotic therapy" 6. However, this refers to the predictive value for finding colorectal neoplasms, not the rate of false positives.

Recommendations for Patients on Eliquis

1. For Colorectal Cancer Screening:

   • Prefer FIT over guaiac-based FOBT when possible
   • No need to discontinue Eliquis before FIT testing 2
   • Be aware that a positive result may be due to anticoagulant-induced bleeding rather than neoplasia
   • Follow up positive results with colonoscopy as recommended by guidelines 2

2. For Diagnostic Purposes:

   • FOBT is not recommended for diagnosis in symptomatic patients or in emergency settings 4, 5
   • Clinical decision-making should not be based on FOBT results alone in patients on anticoagulants

Common Pitfalls to Avoid

1. Using a single-sample FOBT collected during digital rectal examination - this has very poor sensitivity (only 4.9% for advanced neoplasia) 2

2. Repeating FOBT after a positive result instead of proceeding to colonoscopy 2

3. Using FOBT as a diagnostic test rather than a screening tool, especially in emergency settings 4

4. Failing to consider that anticoagulants like Eliquis may cause occult GI bleeding that can lead to positive FOBT results without indicating colorectal neoplasia

In conclusion, while Eliquis can cause false positive results on FOBT due to its potential to cause GI bleeding, FIT testing appears to be less affected by anticoagulant use than guaiac-based tests. For screening purposes, FIT is preferred in patients on anticoagulants, and positive results should always be followed up with colonoscopy.