Lab result explainedInflammationLast updated November 11, 2026

FIT test for colon cancer: what a positive result means, FOBT vs FIT, and how it compares with Cologuard

FIT test (fecal immunochemical test) (FIT) · Stool test (colorectal cancer screening; ordered alone or with hemoglobin and ferritin when anemia is being investigated) · reported in Quantitative FIT: µg hemoglobin per g of feces (µg Hb/g); some platforms report ng/mL of buffer (20 µg/g is about 100 ng/mL on common US systems). Qualitative FIT, gFOBT and Cologuard: positive or negative

A FIT test (fecal immunochemical test) checks a small sample of stool for tiny amounts of blood that you cannot see, using antibodies that recognize human hemoglobin. It is the most widely used stool test for colorectal cancer screening in the US, recommended every year from age 45 to 75 for people at average risk by the US Preventive Services Task Force and the American Cancer Society. A negative result means the hemoglobin concentration was below the lab's cut-off, most often 20 micrograms of hemoglobin per gram of stool (µg Hb/g, equivalent to 100 ng/mL of buffer); a positive result means blood was detected and a colonoscopy is needed to find out where it is coming from.

FIT replaced the older guaiac fecal occult blood test (gFOBT, brand names such as Hemoccult) because it is more accurate and far easier to do. A single FIT detects about 74 to 79 percent of colorectal cancers and about a quarter to a third of advanced precancerous polyps, with a specificity of about 94 percent, so roughly 5 to 8 percent of people screened test positive each round. One sample is enough, no diet or medication changes are required, and because the antibody reacts only to intact human globin, it does not pick up blood from the stomach or from red meat the way guaiac tests did. Cologuard, the multitarget stool DNA test, combines a FIT with DNA markers and is more sensitive (92 percent for cancer) but produces more false positives and is done every three years.

The two things to understand about a positive FIT are that it is common and that it must be followed by colonoscopy, not by a repeat FIT. Out of 100 people with a positive result, about 3 to 5 will have colorectal cancer, 20 to 35 an advanced polyp, around 50 some kind of polyp, and the rest hemorrhoids, diverticulosis, inflammation or no identifiable source. Delaying colonoscopy beyond 9 to 12 months after a positive FIT is associated with a higher chance of cancer and of cancer at a later stage, so the follow-up should happen within a few weeks to months, not be postponed until the next screening cycle.

FIT at a glance

  • What it is: an antibody test for human hemoglobin in stool, used to screen for colorectal cancer and large polyps that bleed intermittently.
  • Who and how often: adults 45 to 75 at average risk, once a year; one sample, no dietary or medication restrictions; people with a family history, inflammatory bowel disease or previous polyps usually need colonoscopy instead.
  • Negative: below the lab cut-off, usually 20 µg Hb/g stool (100 ng/mL). Positive: at or above it. Some labs report the number; higher values carry a higher chance of finding cancer or an advanced polyp.
  • Accuracy: one FIT finds roughly 74 to 79 percent of cancers and 25 to 30 percent of advanced adenomas; specificity about 94 percent. Yearly repetition is what makes the program effective.
  • Positive FIT: colonoscopy, ideally within 1 to 3 months and no later than 6 to 9 months; do not repeat the FIT to 'check'. About 1 in 25 positives is cancer and about 1 in 3 an advanced polyp.
  • FIT vs others: more accurate and simpler than guaiac FOBT; Cologuard is more sensitive (92 percent) but has a 13 percent false-positive rate and is repeated every 3 years; colonoscopy every 10 years remains the most sensitive option.

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What FIT measures

Colorectal cancers and large adenomas have fragile surface blood vessels that bleed intermittently in amounts too small to see, typically 1 to 2 mL of blood a day spread through the stool. FIT uses monoclonal or polyclonal antibodies against the globin part of human hemoglobin. Because globin is digested by enzymes in the stomach and small intestine, the test is largely blind to bleeding from the esophagus, stomach or duodenum and specific to the colon and rectum, which is a feature for screening but means it is not a test for upper gastrointestinal bleeding.

Quantitative FIT, the type used in most US and international screening programs, measures the hemoglobin concentration in a buffer and converts it to µg of hemoglobin per gram of feces. Most US programs set the positive threshold at 20 µg/g; European programs use thresholds from 15 to 47 µg/g to balance colonoscopy capacity against detection. The cut-off matters: lowering it to 10 µg/g catches more cancers but roughly doubles the positive rate. Qualitative FIT kits give only a positive or negative line at a fixed cut-off. Hemoglobin degrades in heat, so samples should be returned within about 2 weeks and not left in a hot car or mailbox in summer; a sample that has degraded reads falsely low.

Guaiac FOBT works differently: hemoglobin's heme group has peroxidase-like activity that turns guaiac paper blue when developer is added. Because animal heme from red meat, plant peroxidases in horseradish, turnips and radishes, and vitamin C (which blocks the reaction) all interfere, gFOBT needs three days of dietary restriction and three separate stool cards, and it detects upper as well as lower gastrointestinal bleeding. Standard Hemoccult II finds only about 30 to 50 percent of cancers; the more sensitive Hemoccult SENSA finds 60 to 80 percent but with more false positives. US guidelines now accept only high-sensitivity gFOBT and prefer FIT. The multitarget stool DNA test (Cologuard, and its 2024 successor Cologuard Plus) adds detection of methylated and mutated DNA shed by tumors to a FIT component and is run on a whole bowel movement.

Normal range for FIT

Reference ranges vary between labs and by age, sex and pregnancy. Use the range printed on your own report.

GroupTypical range (Quantitative FIT: µg hemoglobin per g of feces (µg Hb/g); some platforms report ng/mL of buffer (20 µg/g is about 100 ng/mL on common US systems). Qualitative FIT, gFOBT and Cologuard: positive or negative)Notes
Negative FITBelow the laboratory cut-off, usually below 20 µg Hb/g (below 100 ng/mL)No significant blood detected. Repeat annually. A negative does not guarantee absence of cancer: a single FIT misses about 1 in 4 cancers, which is why it is repeated every year.
Positive FIT20 µg Hb/g or above (100 ng/mL or above) in most US programsAbout 5 to 8 percent of screened people. Colonoscopy is required; a repeat FIT is not an acceptable substitute, even if it comes back negative.
Quantitative result 20–50 µg Hb/gLow positiveStill needs colonoscopy. The chance of cancer is lower (around 2 to 3 percent) but advanced polyps are found in about 1 in 5.
Quantitative result above 100 µg Hb/gHigh positiveRisk rises with the concentration: cancer is found in roughly 8 to 15 percent and advanced neoplasia in 40 to 50 percent at the highest values. These are often prioritized for earlier colonoscopy.
Quantitative result 10–19 µg Hb/gNegative in the US, positive in some European programsBelow the US threshold but above thresholds used in parts of Europe. Not acted on in US screening; some clinicians shorten the interval or discuss colonoscopy if there are symptoms or a family history.
Guaiac FOBT (Hemoccult, three cards)Any blue color on any window = positiveRequires 3 days without red meat, vitamin C over 250 mg, NSAIDs, horseradish or turnips. Standard Hemoccult II misses half or more of cancers; only high-sensitivity versions are guideline-endorsed.
Multitarget stool DNA (Cologuard)Positive or negative composite scoreSensitivity 92 percent for cancer and 42 percent for advanced adenomas, specificity 87 percent (about 13 percent false positives). Repeated every 3 years; a positive needs colonoscopy and is not followed by a FIT.
Not for screeningVisible rectal bleeding, iron-deficiency anemia, change in bowel habit, or high-risk historyThese need direct evaluation, usually colonoscopy, regardless of what a FIT shows. A negative FIT should never be used to reassure someone with symptoms.

Positive FIT test

A positive FIT means human blood was present in your stool at or above the cut-off. It is not a cancer diagnosis: in screening populations, about 3 to 5 percent of positive tests turn out to be colorectal cancer, 20 to 35 percent an advanced adenoma or sessile serrated lesion (polyps with a meaningful chance of becoming cancer over years), and around half any polyp at all. The remainder are explained by hemorrhoids, anal fissures, diverticulosis, colitis, angiodysplasia or no identifiable source. That said, a positive FIT roughly multiplies your chance of having a colorectal cancer by 10 to 20 compared with someone who tested negative, which is exactly why colonoscopy is required.

The only correct next step is a colonoscopy, which both finds the source and removes any polyps during the same procedure. Repeating the FIT is not recommended, because bleeding from polyps and cancers is intermittent: a second test can easily be negative in someone whose first test was a true positive, and a negative repeat does not cancel the first result. CT colonography or flexible sigmoidoscopy are used only when colonoscopy is not possible. If you take anticoagulants or aspirin, the result still counts; these drugs slightly increase the positive rate but the proportion of positives with advanced neoplasia is similar, and guidelines say not to stop them for screening or to disregard a positive result because of them.

Timing matters. In a study of more than 70,000 positive FITs in a US health system, colonoscopy within 8 to 30 days and up to 9 months carried the same cancer risk, but waiting more than 10 months was associated with about a 50 percent higher chance of cancer and a doubling of advanced-stage cancer, and beyond 12 months the risk continued to climb. Most programs aim for colonoscopy within 1 to 3 months; if you have been waiting longer, ask for the referral to be chased. Quantitative values help triage: the higher the hemoglobin concentration, the greater the probability of significant findings.

Common causes

  1. Colorectal cancer

    The reason the test exists. Found in 3 to 5 percent of positive FITs overall, more in men, older people and those with high quantitative values. Most FIT-detected cancers are early stage, when five-year survival exceeds 90 percent.

  2. Advanced adenomas and sessile serrated lesions

    Polyps 1 cm or larger, or with villous or high-grade features, found in 20 to 35 percent of positive tests. Removing them at colonoscopy is what gives FIT programs their 20 to 30 percent reduction in colorectal cancer deaths over time.

  3. Small polyps

    Adenomas under 1 cm bleed less and are found incidentally in another 20 to 30 percent of colonoscopies after a positive FIT; they are removed and set the interval for the next colonoscopy.

  4. Hemorrhoids and anal fissures

    The most common benign explanation. Bleeding is usually bright red and on the paper, but hemorrhoids can cause a positive FIT without any visible blood. They are only accepted as the cause once the colon has been examined.

  5. Diverticulosis and angiodysplasia

    Pouches in the colon wall and fragile vessels, both common after 60, bleed intermittently and are frequent findings when no polyp is seen.

  6. Inflammatory bowel disease, microscopic colitis and infectious colitis

    Any inflamed colon lining leaks blood. A positive FIT with diarrhea, urgency or mucus points toward colitis; fecal calprotectin and biopsies at colonoscopy sort this out.

  7. Menstrual blood, urine contamination or recent rectal bleeding from a procedure

    Collecting during a period, or letting stool contact urine or toilet water with blood in it, can produce a positive. Programs advise waiting 3 days after a period ends and avoiding collection with active hemorrhoid bleeding.

  8. Aspirin, NSAIDs and anticoagulants

    These increase the rate of positive tests modestly by making small lesions bleed more; they do not cause polyps. Guidelines advise against stopping them before FIT and against dismissing a positive result because of them.

  9. Upper gastrointestinal bleeding (rarely)

    Globin is mostly digested before reaching the colon, so FIT is insensitive to ulcers and gastritis, but brisk upper bleeding can still register. Upper endoscopy is considered when colonoscopy is normal and there is anemia or upper symptoms.

Symptoms that can go with it

  • Usually none: FIT is designed to find bleeding that causes no symptoms, and most people with a positive result feel entirely well
  • Visible blood on the stool, in the toilet or on the paper, which should prompt evaluation regardless of the FIT result
  • A change in bowel habit lasting more than a few weeks: new constipation, diarrhea, narrower stools or a feeling of incomplete emptying
  • Unexplained iron-deficiency anemia: fatigue, breathlessness on exertion, pallor, a low hemoglobin and ferritin
  • Abdominal pain, bloating or cramping that is new and persistent
  • Unintentional weight loss
  • Black, tarry stools, which suggest bleeding higher in the gut and need urgent evaluation

Read it alongside

  • Hemoglobin and hematocrit — anemia with a positive FIT raises the likelihood of a significant lesion and makes colonoscopy more urgent.
  • Ferritin and iron saturation — low iron stores indicate chronic blood loss; iron-deficiency anemia in a man or a postmenopausal woman is an indication for colonoscopy whatever the FIT shows.
  • MCV and RDW — a low MCV with a high RDW is the pattern of chronic iron loss from the gut.
  • Fecal calprotectin — distinguishes inflammatory causes of a positive FIT (colitis, Crohn's) from polyps and hemorrhoids.
  • CEA — not a screening test and normal in most early cancers, but measured at diagnosis if a cancer is found, as a baseline for follow-up.
  • Stool culture or GI PCR panel — when a positive FIT comes with acute diarrhea, infection is a possible explanation.
  • Colonoscopy findings — the definitive follow-up; the FIT result is interpreted in light of what the colonoscopy showed and sets the next screening interval.

What usually happens next

  1. If your FIT is negative and you have no symptoms, repeat it in 12 months; a negative FIT does not cover you for longer than a year, and it does not replace evaluation of any new bowel symptoms or anemia.
  2. If your FIT is positive, expect a referral for colonoscopy; aim to have it within 1 to 3 months, and contact your clinician if you have not been scheduled within 2 months. Do not accept a repeat FIT as the next step.
  3. Before colonoscopy, you will be asked about anticoagulants, diabetes medicines and iron tablets (iron darkens the colon lining and is usually stopped a week before), and given a bowel preparation; good preparation matters because it determines whether small polyps are seen.
  4. After colonoscopy, the next screening interval depends on what was found: a normal examination usually means no FIT or colonoscopy for 10 years, one or two small adenomas 7 to 10 years, three or more adenomas or an advanced polyp 3 years, and a cancer a treatment plan with its own surveillance schedule.
  5. If colonoscopy is normal but you are anemic or iron-deficient, ask about an upper endoscopy and, if needed, small bowel imaging, because the colon is not the only possible source.
  6. If you have a first-degree relative with colorectal cancer or advanced polyps, inflammatory bowel disease, or a previous adenoma, FIT is generally not the right screening test for you; colonoscopy at the intervals set for higher risk is recommended instead.

Diet, lifestyle and natural levers with evidence

What can move FIT once the cause is known. Nothing here replaces finding the cause.

Collect the sample at the right time, and skip the diet rules unless it is a guaiac test

Moderate evidence

Nothing you eat or take changes a FIT apart from bleeding itself, so the practical levers are about avoiding false positives and false negatives. Do not collect during menstrual bleeding or within 3 days of it, during a flare of bleeding hemorrhoids, or after a rectal procedure; keep urine and toilet water away from the sample; and return it within 2 weeks, out of heat, because hemoglobin degrades and reads falsely low. For a guaiac FOBT only, avoid red meat, more than 250 mg of vitamin C, horseradish, turnips, radishes and NSAIDs for 3 days before and during collection. Do not stop aspirin or anticoagulants for either test.

Fiber, whole grains and less processed meat

Strong evidence

These lower the chance of developing the polyps and cancers the test is looking for rather than the test result itself. In a BMJ meta-analysis of prospective studies, each 10 g a day of dietary fiber was associated with a 10 percent lower risk of colorectal cancer and three servings a day of whole grains with a 17 percent lower risk. Processed meat is classified by the International Agency for Research on Cancer as a Group 1 carcinogen, with each 50 g daily serving (roughly two slices of bacon) associated with an 18 percent higher risk, and red meat at 100 g a day with about 12 percent higher risk. Dairy and calcium-rich foods are associated with lower risk.

Physical activity and a healthy weight

Strong evidence

Meta-analyses of cohort studies find that the most physically active people have about a 20 to 25 percent lower risk of colon cancer than the least active, independent of weight, and that each 5 kg/m² increase in body mass index raises colorectal cancer risk by around 5 percent in women and 10 percent in men, with abdominal obesity the stronger signal. Activity also improves bowel preparation quality and recovery if a colonoscopy is needed. The usual target is 150 minutes a week of moderate activity plus resistance exercise twice a week.

Limit alcohol and do not smoke

Strong evidence

A meta-analysis of 61 studies found colorectal cancer risk about 20 percent higher with 2 to 3 drinks a day and about 50 percent higher with 4 or more, compared with non-drinkers or occasional drinkers. Long-term smoking raises colorectal cancer risk by around 20 percent and is particularly associated with the serrated polyps that FIT detects poorly, which is one reason smokers are sometimes steered toward colonoscopy. Both also increase the chance of a false-positive FIT through gut irritation and hemorrhoidal bleeding.

Calcium

Moderate evidence

In the Calcium Polyp Prevention Study, 1,200 mg a day of calcium carbonate for 4 years reduced the recurrence of colorectal adenomas by about 15 to 20 percent in people who had already had polyps removed, and observational studies associate higher dairy and calcium intake with roughly 15 to 25 percent lower colorectal cancer risk. A larger later trial of calcium and vitamin D found no benefit, so the evidence is mixed; food sources (dairy, fortified foods, canned fish with bones) are the preferred route.

Calcium supplements above 1,000 mg a day increase kidney stone risk and may raise cardiovascular risk in some analyses; keep total intake from food and supplements under about 2,000 mg and discuss with your clinician if you have kidney disease or a history of stones.

When to see a clinician promptly

  • Black, tarry stools, large amounts of red blood, or bleeding with dizziness, fainting or a racing heart: possible significant gastrointestinal bleeding, which needs emergency care.
  • A positive FIT that has not been followed by a scheduled colonoscopy within 2 months, or any suggestion that you should simply repeat the stool test instead.
  • Rectal bleeding, a persistent change in bowel habit, narrower stools, abdominal pain or unexplained weight loss at any age, even with a negative FIT; symptoms override a screening result.
  • Iron-deficiency anemia found on a blood test, particularly in a man or a woman past menopause, which needs colonoscopy regardless of FIT.
  • A first-degree relative diagnosed with colorectal cancer before 60, or two relatives at any age, or a known hereditary syndrome: you need colonoscopy-based screening starting earlier, not FIT.
  • Severe abdominal pain, fever or bleeding in the days after a colonoscopy with polyp removal, which can indicate perforation or post-polypectomy bleeding.

Frequently asked questions

What happens if my FIT test is positive?

You will be referred for a colonoscopy to find where the blood is coming from and to remove any polyps at the same time. About 3 to 5 in 100 people with a positive FIT have colorectal cancer, 20 to 35 have an advanced polyp, and most of the rest have small polyps, hemorrhoids, diverticulosis or no source found. Aim to have the colonoscopy within 1 to 3 months; waiting more than 9 to 12 months is linked to a higher chance of cancer and later-stage cancer. A repeat FIT is not a substitute.

How accurate is the FIT test for colon cancer?

A single FIT at the usual 20 µg/g cut-off detects about 74 to 79 percent of colorectal cancers and 25 to 30 percent of advanced precancerous polyps, with about 94 percent specificity (6 percent of people without cancer test positive). Because it is repeated every year and cancers take years to develop, the cumulative sensitivity over several rounds is considerably higher, and randomized and program data show 20 to 30 percent fewer colorectal cancer deaths among people screened with stool tests. It is less sensitive than colonoscopy for a single examination, but far more people complete it.

What is the difference between FOBT and FIT?

Both look for hidden blood in stool. The guaiac FOBT uses a chemical reaction with heme that is triggered by animal blood in red meat and by plant peroxidases, and blocked by vitamin C, so it needs 3 days of dietary restriction and three separate stool samples, and the standard version misses half or more of cancers. FIT uses antibodies specific to human hemoglobin, needs one sample with no diet changes, is more sensitive (74 to 79 percent versus 30 to 50 percent for standard guaiac) and is specific to colon and rectal bleeding. US guidelines now recommend FIT or a high-sensitivity guaiac test, and most programs have switched to FIT.

Cologuard vs FIT: which is better?

Cologuard (multitarget stool DNA) detects 92 percent of cancers versus 74 to 79 percent for FIT, and 42 percent of advanced adenomas versus about 25 to 30 percent, but its specificity is 87 percent versus 94 percent, so about twice as many people get a false positive and an unnecessary colonoscopy. It is done every 3 years rather than yearly, requires a whole bowel movement, and costs considerably more. Modeling for the USPSTF found annual FIT and 3-yearly stool DNA offer similar life-years gained. Either is acceptable; the best test is the one you will actually complete on schedule.

Can hemorrhoids cause a positive FIT test?

Yes, hemorrhoids and anal fissures are the most common benign reasons for a positive FIT, and they can cause one without any blood you can see. However, hemorrhoids are so common that they are only accepted as the explanation after colonoscopy has shown there is no polyp or cancer; about a third of people with a positive FIT and known hemorrhoids turn out to have a significant polyp as well. Do not collect the sample while hemorrhoids are actively bleeding, but do not skip the colonoscopy because you have them.

Should I stop aspirin, blood thinners or iron before a FIT test?

No. Aspirin, NSAIDs and anticoagulants slightly increase the chance of a positive FIT, but the US Multi-Society Task Force and screening programs advise against stopping them, because stopping carries its own risks and a positive result on these drugs is just as likely to reflect an advanced polyp. Iron tablets, vitamin C and red meat do not affect FIT (they do affect guaiac FOBT). If you have a positive result, mention these medicines so the colonoscopy can be planned safely.

What does a negative FIT test mean, and can I still have colon cancer?

A negative FIT means less than the cut-off amount of blood (usually 20 µg/g) was in that sample, and your chance of having colorectal cancer right now is low, roughly 1 in 1,000 to 1 in 2,000 in an average-risk screening population. It is not a guarantee: about 1 in 4 cancers and 3 in 4 advanced polyps do not bleed enough to be caught on a single test, which is why FIT is repeated every year. If you develop rectal bleeding, anemia, a change in bowel habit or weight loss, you need evaluation regardless of a recent negative FIT.

At what age should I start FIT testing, and when can I stop?

The US Preventive Services Task Force and the American Cancer Society recommend screening from age 45 for people at average risk, continuing to 75. Between 76 and 85 the decision is individual, based on health, life expectancy and previous screening, and screening is not recommended after 85. People with a first-degree relative with colorectal cancer, inflammatory bowel disease, previous adenomas or a hereditary syndrome should have colonoscopy rather than FIT, often starting at 40 or 10 years before the youngest affected relative's diagnosis.

References

  1. Davidson KW, Barry MJ, Mangione CM, et al.. Screening for colorectal cancer: US Preventive Services Task Force recommendation statement. JAMA (2021)
  2. Lee JK, Liles EG, Bent S, Levin TR, Corley DA. Accuracy of fecal immunochemical tests for colorectal cancer: systematic review and meta-analysis. Annals of Internal Medicine (2014)
  3. Robertson DJ, Lee JK, Boland CR, et al.. Recommendations on fecal immunochemical testing to screen for colorectal neoplasia: a consensus statement by the US Multi-Society Task Force on Colorectal Cancer. Gastroenterology (2017)
  4. Corley DA, Jensen CD, Quinn VP, et al.. Association between time to colonoscopy after a positive fecal test result and risk of colorectal cancer and cancer stage at diagnosis. JAMA (2017)
  5. Imperiale TF, Ransohoff DF, Itzkowitz SH, et al.. Multitarget stool DNA testing for colorectal-cancer screening. New England Journal of Medicine (2014)
  6. Imperiale TF, Porter K, Zella J, et al.. Next-generation multitarget stool DNA test for colorectal cancer screening. New England Journal of Medicine (2024)
  7. Wolf AMD, Fontham ETH, Church TR, et al.. Colorectal cancer screening for average-risk adults: 2018 guideline update from the American Cancer Society. CA: A Cancer Journal for Clinicians (2018)
  8. Fecal occult blood test (FOBT). MedlinePlus, US National Library of Medicine (2023)View source
  9. Colorectal cancer screening (PDQ): health professional version. National Cancer Institute (2024)
  10. Aune D, Chan DS, Lau R, et al.. Dietary fibre, whole grains, and risk of colorectal cancer: systematic review and dose-response meta-analysis of prospective studies. BMJ (2011)
  11. Fedirko V, Tramacere I, Bagnardi V, et al.. Alcohol drinking and colorectal cancer risk: an overall and dose-response meta-analysis of published studies. Annals of Oncology (2011)
  12. Baron JA, Beach M, Mandel JS, et al.. Calcium supplements for the prevention of colorectal adenomas. New England Journal of Medicine (1999)

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This page is educational and is not medical advice or a diagnosis. Lab results have to be interpreted together with your history, symptoms and other results by a clinician who knows you. Do not start or stop a supplement to change a lab value before the cause is known.