A faecal pH test is one where a specimen of faeces is tested for acidity in order to diagnose a medical condition.
The pH of human faeces is variable but the average is pH 6.6 (acidic) for normal faeces. A lower faecal pH (very acidic stool) can indicate a digestive problem such poor absorption of carbohydrates or fats, lactose intolerance, an infection such as E. coli or rotavirus, or overgrowth of acid-producing bacteria (such as lactic acid bacteria).