The gFOBT has a long history of use for detecting the presence of blood in the stool and is based on the pseudoperoxidase
activity of heme in human hemoglobin.
This method detects the pseudoperoxidase
activity of hemoglobin; thus, endogenous salivary peroxidases produce false-positive results for hemoglobin.
Ascorbic acid as an antioxidant may yield false negative results when it interferes with the pseudoperoxidase
It is also relevant to mention that above-therapeutic concentrations of mesna, which carry a high reducing capacity, did not cause interference in two Chemstrip 10UA tests that are based on oxidation reactions (glucose by glucose oxidase/peroxidase and hemoglobin with its strong pseudoperoxidase
A second obstacle was the pseudoperoxidase
activity of hemoglobin, which can catalyze side reactions with hydrogen peroxide.