This test is done to determine the cause behind problems in the stomach, intestines, or other parts of the gastrointestinal (GI) system. A stool culture helps the doctor see if theres a bacterial or parasitic infection in the intestines. Normal stool pH is 7.0 to 8.0. A high level of reducing substance in the stool suggests the presence of conditions such as lactase deficiency, short bowel syndrome, and carbohydrate malabsorption.Stool pH <6.0 is suspected of lactase enzyme deficiency.