The stool fat (or fecal fat) absorption test measures the amount of fat in your stool, or bowel movement. If you have too much fat in your stool, it’s an indication of malabsorption, which can indicate a variety of digestive diseases or cystic fibrosis.

You will be asked to collect either a single stool sample or a small amount of stool from all bowel movements over a two- to four-day period for analysis in a lab.