Warfarin & Fecal Occult Blood Tests: Can They Be Combined?

Question
My husband is taking Warfarin and his doctor says it's okay for him to take one of those occult blood in the stool tests, the Warfarin won't give him a false positive. What do you say?


Answer
Hello Loretta,

I say he's right.  Anti-coagulants, like coumadin, do not cause bleeding themselves (at appropriate doses).  Certainly they can can exacerbate an active bleed or perhaps finish off an unstable clot.  

Hemoccult tests do get false positives though.

Drugs shown to be associated with gastrointestinal blood loss in normal subjects include salicylates (aspirin), steroids, all nonsteroidal anti-inflammatory drugs, and colchicine.  These agents differ from warfarin in that they are GI irritants (also aspirin has a anti-platelet quality too).  False-positive results may be caused by excessive dietary intake of certain vegetables, especially horseradish, and red meats because of the possibility of having residual red blood in the colon.

Vitamin C  and antacids may cause false- negatives to hemoccult tests.

When occult GI bleeding is suspected, at least three samples, from separate bowel movements, should be submitted.   

Thank you for the question, I apologize for the delay.

Dr.T