Your fecal lactoferrin came back positive. Now what?

If you're reading this late at night with the report open, start here. A positive result has several possible causes, and the test cannot tell them apart. What it did was tell your doctor that something in your gut is inflamed and worth a closer look.

For the basics of how the test works, see what the lactoferrin stool test measures. This page is about the result you actually have.

Is lactoferrin in stool bad?

Having some lactoferrin in your stool is normal. Healthy people carry a small amount, and so do people with irritable bowel syndrome. A result above the lab's cutoff means your intestines are inflamed. That is worth looking into, and on its own it is not a diagnosis of anything.

The result is useful without being good or bad. A raised level means the test found the thing it looks for, which is why your doctor ordered it. Whether it turns out to matter much is a separate question, and one positive result is not enough to answer it.

If your report carries a number, the figures labs measure in healthy people, in IBS and in active disease are set out in the normal range for lactoferrin in stool. Healthy volunteers and people with IBS both averaged around 1 µg/g in the assay maker's own validation study, well below the 7.2 µg/g cutoff.

Does a positive result mean cancer?

No. The test was designed to spot inflammation, and doctors do not use it to screen for bowel cancer.

There is one finding you may come across, so here it is plainly. A 2024 study of 104 patients in Japan found lactoferrin levels tended to run higher in people with bowel growths, including cancer, than in healthy people. But in the same study, a test for hidden blood in stool did the better job of finding cancer. That is the kind of test used for bowel cancer screening. Lactoferrin rises with many kinds of gut trouble, so a positive result on its own cannot point to any one of them.

What causes positive lactoferrin in stool

Inflammation somewhere in your intestines. Labcorp, which runs the quantitative version of this test, names gut infections, Crohn's disease, ulcerative colitis, celiac disease and colorectal cancer among the conditions that raise it. The test reacts to the inflammation and not to its cause, so it cannot tell you which of those produced your result.

The lab is detecting lactoferrin, a protein carried inside white blood cells. When those cells gather in the lining of your intestines, some of them break down and the protein ends up in your stool. ARUP, one of the large US reference labs, describes a positive result as a marker for white blood cells in the stool, and nothing more specific than that.

Several things can bring those cells in:

• A gut infection. Bacteria, viruses and parasites all set off this response. A 2015 review found stool markers like lactoferrin help alongside other tests, but lack the accuracy to diagnose an infection on their own. If your symptoms started suddenly, your doctor may order a stool culture or a panel that looks for germs directly.
• Inflammatory bowel disease. That means Crohn's disease or ulcerative colitis, where the immune system keeps the bowel lining inflamed over months or years. Telling these apart from irritable bowel syndrome (IBS) is one of the main reasons the test gets ordered.
• Celiac disease. An immune reaction to gluten that inflames the small intestine. Labcorp lists it among the conditions that raise the result.
• Bowel growths, including cancer. The section above covers why lactoferrin is still not the test used to look for these.
• Other kinds of inflammation. Whatever the source, the response is the same, and the result looks the same. It cannot say where in the intestines the inflammation is, or why it is there.

How long you have been unwell narrows that list more than the list itself does. A positive result a week after a bout of food poisoning and the same result after four months of symptoms point in different directions. The clinician who ordered the test is the one who knows which of those describes you.

What can push the result up without gut inflammation

A few things, and each one changes how much weight your number deserves.

A lactoferrin supplement, but only one kind. This assay is built to find human lactoferrin. Bovine lactoferrin, the kind in dairy and in nearly every supplement sold, is a structurally different protein, and Labcorp states its test does not detect it. Human lactoferrin is the exception: Labcorp warns that people taking a human lactoferrin supplement carry a risk of a false positive. Recombinant human lactoferrin is now made at industrial scale, so tell whoever ordered the test what you have been taking. For the difference between the two, see what a lactoferrin supplement label does and does not tell you.

Breast milk. Human milk carries a lot of lactoferrin, and Labcorp flags the same false-positive risk for nursing infants. A healthy breastfed baby's stool runs so far above an adult cutoff that the comparison is barely meaningful, and what lactoferrin in stool is gives the measured figures. Formula is the other case and it runs the other way, because the cow lactoferrin that goes into lactoferrin in baby formula is not picked up by this assay at all.

Which part of the sample reached the analyzer. Labcorp states that lactoferrin is not spread evenly through stool, and that differences in sampling can change the measured concentration, most of all when the level is high. That is one reason a repeat test can read differently with nothing about you having changed.

Labcorp also lists groups the test may not suit at all: people who are immunocompromised, people with a history of HIV or hepatitis B or C, anyone who has had infectious diarrhea in the past six months, and anyone who has had a colostomy or ileostomy within the past month. If one of those fits you, ask why this test was chosen.

Is lactoferrin positive with C. diff?

Usually, yes. A Clostridioides difficile infection inflames the colon, which is the thing this test detects, so a positive result in someone with C. diff is the expected finding.

What the result will not do is name C. diff as the cause. That takes a test which looks for the bacterium or its toxins directly.

Two studies show how far the number gets you. A Stanford group measured fecal lactoferrin in 118 patients who tested positive for C. difficile by PCR: 59 with clinically significant diarrhea, meaning three or more episodes in 24 hours, and 59 without. Lactoferrin ran higher in the significant-diarrhea group, a median of 99.0 against 55.1 µg/mL. The authors still concluded the measurement could not sort patients into the two groups well enough to use.

A Madrid hospital asked a different question of 170 confirmed infections: does the level at diagnosis predict what happens next? Levels were higher in the patients who went on to a severe episode or a recurrence. The threshold that predicted recurrence best was 6.0 µg/mL, below the 7.2 µg/mL the assay maker proposes, and the numbers it produced were modest even then. The authors put it forward as something to add to the clinical scores doctors already use, rather than a test to lean on by itself.

How much one result can tell you

Less than it might seem, and that is worth knowing before you assume the worst.

When researchers pooled studies on telling IBS apart from inflammatory bowel disease in adults, only two lactoferrin studies met their standards. They concluded that lactoferrin on its own was of little clinical use for that job. Calprotectin, a similar stool test, and a blood test called C-reactive protein did better. That is one reason your doctor may repeat the workup with a different test before drawing any conclusion. For what separates the two stool markers, including why only one of them gets a number to read against, see lactoferrin vs calprotectin.

Results can also mislead in the other direction. ARUP's own guidance says a negative result does not rule out inflammation. The assay maker's own validation study puts a figure on that gap, and on how often an elevated result is right: see how accurate the lactoferrin stool test is, including the assessment those percentages were measured against.

If your report carries a number rather than the word positive, see the normal range labs use for lactoferrin in stool, where the cutoff comes from, and how much the same sample can vary between runs.

Does a higher number mean worse disease?

Not in a way you can read off the report. A result four times the cutoff does not mean your condition is four times as serious, and neither Labcorp nor ARUP publishes a scale that turns micrograms into a severity grade.

The strongest sign of that comes from the main US guideline on using these markers. In 2023 the American Gastroenterological Association published its recommendations on using stool and blood markers to manage ulcerative colitis. For fecal calprotectin, a similar stool test, the panel put numbers in the recommendations themselves: under 150 µg/g to rule out active inflammation, above 150 µg/g to inform a treatment decision. For fecal lactoferrin it set no threshold. The recommendations say "normal" and "elevated" and stop there.

So two things carry weight: whether your result cleared the cutoff, and what your symptoms are doing. How far it cleared the cutoff is not one of them. Repeat runs of the same sample vary by about a third in any case, which is covered in why the same sample can give two different numbers.

One limit on all of that. The AGA guideline is about people who already have a diagnosis of ulcerative colitis. If this is your first lactoferrin test and nobody has diagnosed you with anything, it was not written about you. All seven of its recommendations are conditional ones rather than strong ones.

If you already have Crohn's disease or colitis

Here the test has a different job: checking whether your disease is active. A 2020 analysis combined 10 studies covering 773 people with inflammatory bowel disease.

For ulcerative colitis, the test caught active disease in about 8 of every 10 people who had it. It also came back negative for about 8 in 10 people whose disease was quiet. For Crohn's disease it caught active disease about as well, but only about 7 in 10 people with quiet disease tested negative. Put plainly, for 2 or 3 people in 10 whose Crohn's is under control, the test still reads positive.

So a single positive result during treatment does not prove a flare. Your gastroenterologist will weigh it against how you feel and, often, other tests.

The AGA guideline builds that into its advice, for ulcerative colitis only. If your symptoms have settled, a normal lactoferrin result supports leaving the treatment alone and skipping a routine camera test. If your symptoms are moderate or severe and the marker is elevated, it supports acting on that without one. When the two disagree, in either direction, the panel suggests looking with a camera instead of trusting the marker. Where symptoms are only mild, it suggests endoscopy to inform the decision. None of those recommendations covers Crohn's disease, which the panel did not review.

Questions to take to your appointment

You don't need to know what your result means before you go. You need to leave knowing what happens next. These questions help:

• Why did you order this test, and what were you looking for?
• Does my lab report a number, or only positive or negative?
• Could an infection explain this? Do I need a stool culture?
• Would a fecal calprotectin test or a blood test add anything?
• Do I need a colonoscopy, and if so, how soon?
• What symptoms should make me call before then?

Bring the printed report, so whoever reads it can see exactly which test the lab ran and how it reported the result. If you are asked to give another sample, how you collect it and how long the lactoferrin stool test takes both depend on which of the two versions your lab runs.