What it is: A fecal fat test measures the amount of fat in stool to detect steatorrhea (excess fat excretion), using either a quick qualitative stain (Oil Red O) or a quantitative 72-hour timed collection.
Why it's ordered: Ordered for symptoms of malabsorption — persistent diarrhea, greasy or foul-smelling floating stools, unexplained weight loss, or fat-soluble vitamin deficiencies (A, D, E, K) — and to work up suspected pancreatic exocrine insufficiency, celiac disease, Crohn's disease, short bowel syndrome, or bacterial overgrowth.
What it detects: Excess fecal fat, which signals a breakdown somewhere in fat digestion — pancreatic enzyme production, bile acid emulsification, or intestinal absorption — without identifying which stage failed.
Collection & prep: The quantitative version requires a 72-hour timed stool collection while eating a standardized ~100g/day fat diet for 2–3 days before and during collection; a dietary log is used to calculate the coefficient of fat absorption. The qualitative version uses a single random sample.
Results:
Elevated – typically >7g fat/24 hours; suggestive of malabsorption but doesn't identify the cause
Normal – doesn't fully exclude malabsorption, especially if diet wasn't followed correctly during collection
Possible complications of fat malabsorption: Untreated malabsorption can lead to fat-soluble vitamin deficiencies and unintended weight loss. The test itself is burdensome — the multi-day collection and dietary requirements are cumbersome, which can affect patient compliance and result accuracy, and abnormal results usually prompt further testing (e.g., pancreatic elastase, imaging) to pinpoint the cause.
Statements made in the Clinical Manual have not been evaluated by the FDA. The products mentioned are not intended to diagnose, treat, cure or prevent any disease.
