Evaluation of the guaiac fecal occult blood test for detection of gastrointestinal bleeding in the rhesus macaque (Macaca mulatta)

Background Gastrointestinal (GI) hemorrhage accompanies several common diseases of rhesus macaques (Macaca mulatta). Guaiac fecal occult blood testing (gFOBT) is a non‐invasive means to detect such bleeding in several species; however, there are currently no data indicating reliability of this test to detect GI hemorrhage in macaques. Methods We evaluated sensitivity and specificity of gFOBT to detect simulated and biopsy‐associated bleeding in the stomach, duodenum, and colon of 15 rhesus macaques. Fecal samples were analyzed via gFOBT for 72 hours. Results Guaiac fecal occult blood testing was more sensitive to detect lower vs upper GI bleeding; sensitivity was volume‐dependent in the upper GI tract. Single‐test specificity was 95.2%. Repeated fecal collections increased gFOBT sensitivity without affecting specificity. Conclusions Guaiac fecal occult blood testing is a useful screening test for both upper and lower GI bleeding in rhesus macaques. For highest sensitivity, gFOBT should be performed on three fecal samples collected 24 hours apart.