What Causes Red Blood In The Stools For My 4-year-old Son?

My son is 4 years and 5 months old. From last two months, we observe red blood in stool sometimes. I gave stool sample for test. Its colour is brown, having semi solid consistency and the absence of mucus and blood, as said in the report. Chemical examination of the stool test says that the reaction is acidic while microscopic examination says that ova, cyst, epithelial cells and pus cells are absent. Red blood cell is 2-3. Macrophages is absent and undigested starch/fat and vegetable fibres are present. Occult blood is detected in the stool. Pl inform what are the causes behind these irregularities in the stool .