What is a Faecal Fat Test? Procedure & Results Explained

Last updated: 13 December 2017

What is a faecal fat test?

A faecal fat test is a laboratory test that measures the amount of fat in faecal samples (stools).

It may be used to confirm a diagnosis of malabsorption, where fats and oils are not properly absorbed by the gastrointestinal system.

Faecal fat test is a test on the stools to measure the amount of fat in them. Usually, the body absorbs and digests fat very efficiently and there is no fat remaining in the stools.

When normal absorption is affected, for example by diseases affecting the intestine or pancreas, so-called malabsorption results in stools which are oily or greasy, bulky and difficult to flush – steatorrhoea.

The absorption of fat-soluble vitamins including vitamins A, D, E, and K can be affected because these vitamins are dissolved in dietary fat and are therefore absorbed along with fats.

How is a faecal fat test performed?

The faecal fat test is a rather unpleasant procedure, which involves collecting 3 full days’ worth of faeces in a bucket with a lid, while consuming at least 100 grams of fat per day.

The stool collection is then analysed in a laboratory. It is not really a necessary test when there is obvious fat malabsorption, but may be helpful in less obvious cases.

This test rather unpopular and is rapidly being replaced by other tests of pancreatic function.

Faecal fat test results explained

Faecal fat tests may be reported as negative or positive.


A negative faecal fat test results indicates that all fat absorbed by the body and none atr remaining in stools, or normal.


A positive faecal fat test results indicates an incomplete absorption of fat.

The amount of lipid (fat) per 24 hours may be stated – this should normally be less than 20 mmol.

Related specialists

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Also known as

  • Fecal fat test
  • Stool fat test
  • Fat digestion test



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This article is for informational purposes only and should not be taken as medical advice. If in doubt, HealthEngine recommends consulting with a registered health practitioner.