Lactoferrin in stool: what the test means

Why this test exists

Lactoferrin is stored inside neutrophils, a type of white blood cell. When those cells move into the lining of your intestine, which is what happens during inflammation, some of them break open and release what they were carrying. That material ends up in stool, where a lab can measure it.

So the test is not looking for lactoferrin because lactoferrin is a problem. It is using lactoferrin as a tracer for white blood cell activity in your gut.

What a positive result narrows down

Its most common use is telling inflammatory bowel conditions apart from irritable bowel syndrome. Both cause pain, urgency and disrupted bowel habits, and from the outside they can look similar. Inflammatory conditions involve actual inflammation of the bowel wall. IBS, for all the misery it causes, generally does not.

A positive result pushes toward the inflammatory side, which usually means more investigation. A negative result is often the more immediately useful of the two, because it can spare someone a colonoscopy.

What the guidelines say about it

The American College of Gastroenterology tells doctors to check either fecal calprotectin or fecal lactoferrin, alongside a C-reactive protein blood test, when someone has suspected IBS with diarrhea and no alarm features, specifically to rule out inflammatory bowel disease. So the test is doing a recognized job, and that is the job it is doing for you.

There is a detail in that guideline worth knowing, because most sites leave it out. The recommendation is rated strong either way, but the quality of evidence behind it differs by which marker is used: moderate for calprotectin and C-reactive protein, and very low for fecal lactoferrin. Calprotectin is simply the better-studied of the two.

That does not make your result meaningless. It does mean a lactoferrin result is a prompt to look further rather than a verdict, and it is one reason your doctor may want a different test as well.

What it does not tell you

It does not name a condition. Inflammation has many causes, including infections and some medications, and the test cannot tell them apart.

It does not measure how bad things are in any way you can read off the number yourself. Labs run this test differently: some report it simply as positive or negative, others give a number in micrograms per gram, and the cutoff is not the same everywhere. A value from one lab does not transfer to another.

It is not a cancer screen. If that was your first thought on seeing the result, it is an understandable one, and it is not what this test is for.

What usually happens next

Typically a conversation, then possibly more tests. Depending on your symptoms and history, that can mean blood tests, stool cultures to rule out infection, or referral for a camera test to look at the bowel directly and take samples.

Bring the actual report to the appointment, including the number and the units, because the reference range depends on which test the lab ran.