Do Nosebleeds Cause Stool Blood Tests to Become Positive?

As a general rule, an ordinary nosebleed will not cause a screening stool blood test (hemoccult or guaiac) to come back positive.

However, if the nosebleed is bad enough to consider going to the emergency room... and you are swallowing a lot of it... only than will it be likely that such stool tests will come back positive for blood.

To be precise, such stool tests turn positive only if there's at least 2+ teaspoons of blood leaking into the digestive system everyday (or swallowed from a very bad nosebleed).

Of course, there are MUCH more sensitive tests out there to determine if there's blood in the stool including heme-porphyrin or immunochemical tests, but have a high false-positive rate.

From an ENT perspective, immunochemical testing is interesting because this test uses antibodies to detect human globin epitopes which get digested in the stomach... so if there's a question of whether a patient's anemia is due to nosebleed or a lower GI tract bleed (ie, colon), immunochemical stool testing can answer the question.

Just as an FYI, if the nosebleed is severe, it is likely that you will end up getting your nose packed.