Backgrounds: Fecal occult blood testing (FOBT) is commonly used in colorectal cancer screening programs. Many studies have compared different FOBT methods, but the correlation between traditional red cell microscopy and FOBT remains unclear. Objectives: 1) To evaluate the rate of positive FOBT in patients with different disease groups; 2) To compare the sensitivity and specificity of red blood cells detection in fresh stool by microscopy technique and FOBT. Materials and methods: This was a cross-sectional study involving 120 patients from Hue University of Medicine and Pharmacy Hospital who requested a stool test from 4/2021 to 4/2022. Fresh stool samples were examined for the presence of red blood cells using traditional microscopy and FOBT technique. Results: The overall positivity rate of FOBT was 20%, and in the group of gastrointestinal diseases (n = 24), clinical anemia (n = 21), hepatobiliary diseases (n = 26) and other diseases (n = 49), it was 37.5%, 23.8%, 11.5% and 14.3%, respectively. In comparison with the FOBT technique, microscopic RBC detection had a sensitivity of 33.3% and a specificity of 100%. Conclusions: A high rate of fecal occult blood tests was observed in patients with gastrointestinal disorders. Microscopic erythrocyte detection has low sensitivity and many disadvantages compared to the rapid test. This rapid test should be widely used in clinical practice to aid in the diagnosis of gastrointestinal bleeding