The guaiac-based fecal occult blood test in healthy dogs: Evaluation of the effects of diet, and the ability of the test to detect fecal occult blood

Background: The guaiac-based fecal occult blood test (gFOBt) has been used for human colorectal cancer screening. It can detect the fecal occult blood (FOB) in dogs after oral administration of 20 mg of hemoglobin/kg body weight of blood and is influenced by diet. Objectives: The aims were to evaluate the effect of diet and the ability of gFOBt to detect FOB in healthy dogs after oral administration of autologous blood. Methods: Five healthy dogs were fed Purina Hypoallergenic (HA) and Gastrointestinal (EN) diets. Feces were tested with gFOBt before starting diets and at each defecation (hereafter referred to as fecal collection event) throughout the study period. Every 4 days, increased doses of autologous blood were administered orally. The whole blood of one dog was progressively diluted with a saline solution, and dilutions were directly tested with the gFOBt, until a negative result was found. Results: Twelve of 185 (6.5%) gFOBt were found to be positive. No associations between diet and gFOBt positivity were found. A significant association was found between the fecal collection event and gFOBt positivity (P <.001) and between doses of blood and gFOBt positivity (P =.048). The lowest dilution ensuring all positive tests was 6.5 µgHgb/mL. Conclusions: The gFOBt was not influenced by either the HA or EN diets. The gFOBt positivity was associated with the dose of blood and the fecal collection event. However, caution is needed in the interpretation of results due to the lack of an association between gFOBt positivity and increasing doses of blood in the same dog.