FIT looks for blood
FIT stands for faecal immunochemical test. A small sample of poo is sent to a laboratory, which checks for haemoglobin, a protein in human blood. The amount of blood can be too small to see.
Blood can come from bowel cancer, polyps, inflammation, haemorrhoids (piles) or other causes. FIT cannot tell us where the blood came from or what caused it. A positive result means further assessment is needed, not that cancer has been diagnosed.
Where is FIT used?
Bowel cancer screening
The National Bowel Screening Programme uses FIT in eligible people without bowel symptoms. Testing is offered every two years, with colonoscopy usually arranged after a positive result. This is a practical way to look for early bowel cancer across a large population.
Prioritising investigation of symptoms
FIT is now also used in New Zealand to help assess people with bowel symptoms. The national pathway began rolling out in July 2026. The result helps services identify who may need investigation sooner. Symptoms, examination and blood tests still influence the decision, even when FIT is negative.
NZ screening ages, as at 15 October 2026
Free routine screening is offered to eligible people aged 56 to 74 in eight districts, including all three Auckland districts. In the rest of New Zealand, the age range is currently 58 to 74.
Districts and other eligibility details
The eight districts are Waitematā, Auckland, Counties Manukau, Waikato, Tairāwhiti, Wairarapa, West Coast and South Canterbury.
You must also be eligible for publicly funded health care. Some Māori and Pacific people who joined earlier screening pilots continue to receive invitations at a younger age. The starting age is changing, so check the current programme information if you are unsure.
A previous negative screening test does not settle a new problem with bowel symptoms.
Screening eligibility and your individual assessment
The age for a public screening invitation is not the age below which bowel disease is impossible. If you have symptoms, a relevant family history or previous polyps, I assess those concerns separately from programme eligibility.
If you are well and interested in screening before you qualify for the New Zealand programme, discuss the options with me or your GP. Some overseas programmes and recommendations start at 45. Colonoscopy and regular validated FIT are different options, with different benefits, limitations, costs and follow-up. An overseas recommendation does not establish New Zealand public funding.
Returning the kit and checking the result
A FIT pathway is only complete when the sample has been returned, a result is available and the next step has been agreed. If you cannot complete the kit or have not received your result, contact the team that arranged it. A low result makes bowel cancer less likely, but it does not explain persistent bleeding, iron deficiency or a continuing change in bowel habit. Arrange a review with your GP if symptoms persist or change. Follow any specific instructions from the endoscopy service.
Why do screening ages differ overseas?
These ages concern routine screening for people without symptoms at average risk. Programme eligibility and a clinical recommendation are different. The comparison does not decide which test you personally need. Scroll across the table on a small screen.
| Setting | Programme or recommendation? | Age | Test and access |
|---|---|---|---|
| New Zealand | Public National Bowel Screening Programme | 56 to 74 in eight districts, including all three Auckland districts. 58 to 74 elsewhere. | FIT every two years. New invitations follow the staged rollout and usual birthday cycle. |
| Australia | Public National Bowel Cancer Screening Program | 45 to 74 | FIT every two years. Ages 45 to 49 request the first kit; ages 50 to 74 are mailed kits. |
| England | NHS public programme. Other UK nations have their own arrangements. | 50 to 74 for routine invitations. Age 75 and over can request kits. | FIT every two years. During expansion, the first invitation may arrive at 50, 52 or 54. |
| United States | USPSTF clinical recommendation, rather than one national invitation programme | 45 to 75 routinely. Ages 76 to 85 are an individual decision. | Several options, including annual FIT or colonoscopy every ten years after a normal screening examination. |
Symptoms, previous polyps, inflammatory bowel disease and relevant family history can need a different plan, regardless of programme age. International recommendations do not determine New Zealand public funding.
Why can FIT miss precancerous polyps?
FIT relies on a lesion releasing enough blood into the sample. Not all precancerous polyps bleed, and some cancers bleed only intermittently. This is particularly relevant to flat serrated polyps, which can release very little blood.
A substantial proportion of higher-risk precancerous lesions can therefore be missed by a single FIT. The example below shows this limitation. It does not estimate your own chance of having a polyp or cancer.
What FIT can tell us, and what colonoscopy adds
Choose a view to explore how the tests work. You can also open the text explanation below.
A polyp can be present even when FIT is negative
Some precancerous polyps bleed very little, or do not bleed when the sample is taken. FIT is less reliable for finding these lesions than it is for finding bowel cancer.
Imagine 100 people who already have an advanced precancerous lesion.
In one international screening study, a single FIT was positive in about 23 of these 100 people. About 77 had a negative FIT.
23 positive FIT results
77 negative FIT results
This is not your chance of having a polyp after a negative result. Every person in this example already had a lesion found on colonoscopy.
These are rounded results from one FIT round in a US screening study published in 2024, using a positive result above 20 micrograms of haemoglobin per gram of stool. The lesions included advanced adenomas and sessile serrated lesions at least 1 cm in size. Figures vary with the test and cut-off used. This is not an estimate of accuracy in the New Zealand symptomatic FIT pathway. BLUE-C study, 2024.
FIT looks for human blood in a small poo sample
FIT measures haemoglobin, the protein that carries oxygen in blood. It can detect traces of blood that you cannot see.
The result can help prioritise investigation for possible bowel cancer. It does not show where the blood came from or look directly at the lining of the bowel.
A positive result can have several causes. The next step depends on why you had the test and the advice given with your result.
A polyp can be present even when FIT is negative
Some precancerous polyps bleed very little, or do not bleed when the sample is taken. FIT is less reliable for finding these lesions than it is for finding bowel cancer.
Imagine 100 people who already have an advanced precancerous lesion.
In one international screening study, a single FIT was positive in about 23 of these 100 people. About 77 had a negative FIT.
23 positive FIT results
77 negative FIT results
This is not your chance of having a polyp after a negative result. Every person in this example already had a lesion found on colonoscopy.
These are rounded results from one FIT round in a US screening study published in 2024, using a positive result above 20 micrograms of haemoglobin per gram of stool. The lesions included advanced adenomas and sessile serrated lesions at least 1 cm in size. Figures vary with the test and cut-off used. This is not an estimate of accuracy in the New Zealand symptomatic FIT pathway. BLUE-C study, 2024.
Colonoscopy looks directly at the bowel lining
Colonoscopy is the reference examination for finding polyps in the large bowel. It also allows most polyps to be removed and tissue samples, called biopsies, to be taken.
Biopsies can help diagnose conditions that FIT cannot identify, including bowel inflammation. The laboratory examines the tissue to identify what it is.
Colonoscopy is the gold-standard examination of the large bowel, but it is not perfect. Good bowel preparation and a careful, complete examination improve detection. When I advise further investigation, I consider your symptoms, blood tests, previous examinations and general health.
Read all three explanations as text
1. FIT looks for blood
FIT measures human haemoglobin, the protein that carries oxygen in blood. It can detect small traces of blood in a poo sample that you cannot see. The result can help prioritise investigation for possible bowel cancer. It does not show where the blood came from or look directly at the bowel lining.
2. What FIT can miss
Some precancerous polyps bleed very little, or do not bleed when the sample is taken. A polyp can be present when FIT is negative.
In one international screening study, a single FIT was positive in about 23 of every 100 people who already had an advanced precancerous lesion. About 77 of these people had a negative FIT. Every circle in the visual represents a person already known to have a lesion. The 23 navy circles represent positive FIT results. The 77 outlined circles represent negative results.
This is a rounded result from one FIT round in a US screening study published in 2024, using a positive result above 20 micrograms of haemoglobin per gram of stool. This is not your risk of having a polyp after a negative result. The lesions included advanced adenomas and sessile serrated lesions at least 1 cm in size. Figures vary with the test and cut-off used. These screening results are not an estimate of accuracy in the New Zealand symptomatic FIT pathway. BLUE-C study, 2024.
3. What colonoscopy adds
Colonoscopy looks directly at the lining of the large bowel. It is the reference examination for finding polyps and allows most polyps to be removed. It also allows tissue samples, called biopsies, to be taken. Biopsies can help diagnose conditions that FIT cannot identify, including bowel inflammation.
Colonoscopy is the gold-standard examination of the large bowel, but it is not perfect. Good bowel preparation and a careful, complete examination improve detection. When I advise further investigation, I consider your symptoms, blood tests, previous examinations and general health.
Where do the 23 and 77 figures come from?
In a large US screening study published in 2024, 2,144 people had advanced precancerous lesions found at colonoscopy. FIT was positive in 500 of them (23.3%). The remaining 1,644 (76.7%) had a negative FIT in that screening round.
Advanced precancerous lesions are higher-risk findings, such as larger adenomas or serrated lesions, or adenomas with more advanced cell changes. They are not the same as invasive cancer, and they do not all go on to become cancer.
The study used one commercial FIT, with results above 20 micrograms of haemoglobin per gram of stool counted as positive. Detection varies with the test, cut-off and population. These figures are not the exact performance of repeated NZ bowel screening or the NZ symptomatic pathway. They describe people who already had these lesions, not all people with a negative FIT.
FIT is still useful. Taking part in recommended screening offers an opportunity to find a problem that might otherwise go unnoticed. Its benefit depends on returning the kit, repeating screening when invited, and completing follow-up after a positive result. For people with symptoms, it helps prioritise assessment rather than providing a complete check of the bowel.
What does colonoscopy add?
Colonoscopy is the gold standard for examining the lining of the colon and finding polyps. The scope is a flexible tube with a camera at its tip. Many polyps can be removed during the same examination, and biopsies can be taken when needed.
Colonoscopy and biopsies can also help diagnose bowel inflammation and other conditions that FIT cannot identify. FIT cannot show the bowel lining, establish the type of polyp or remove it.
| What the test does | FIT | Colonoscopy |
|---|---|---|
| Finds polyps | Uses blood as an indirect clue. Many polyps do not cause a positive result. | Looks directly at the bowel lining. |
| Removes polyps | No. | Many can be removed during the examination. |
| Checks abnormal tissue | Cannot take a biopsy or establish a tissue diagnosis. | Can take biopsies to diagnose cancer, inflammation and other conditions. |
Colonoscopy is generally very safe. Serious complications are uncommon, and perforation (a hole in the bowel wall) is very rare. The risk varies with your health and any treatment needed, particularly removal of a large or complex polyp. I will discuss the risks relevant to your examination. Good bowel preparation and careful inspection help find polyps, although no examination detects every lesion.
FIT has an established role as the first test in routine population screening. However, a negative FIT does not replace a colonoscopy recommended for persistent symptoms, polyp follow-up, a previous bowel cancer or another clinical concern.
Understanding a FIT result
Open a result for a short explanation.
Positive FIT
The result is at or above the cut-off, so blood was found in the sample and further assessment is recommended. This is often a colonoscopy, although a scan or specialist review may suit your situation better. Your symptoms and the reason for testing help decide how soon you need assessment. Do not assume piles or blood-thinner medicines explain the result.
Negative FIT
Blood was below the test’s cut-off. This reduces the likelihood of bowel cancer, but cannot reliably exclude precancerous polyps or every cause of bowel symptoms. In routine screening, people are normally invited again in two years if still eligible. If symptoms persist, recur or worsen, seek review rather than waiting for the next screening test.
No valid result
If you did not return the kit or the laboratory could not process it, there is no result. The test has not ruled anything out. Contact the service that arranged it about a replacement kit. If you were expecting a result and it has not arrived, contact that service rather than assuming the test was negative.
If you receive a test kit
If the test is sent through the National Bowel Screening Programme (NZBSP), instructions for collecting and returning the sample will come with the kit. Follow those instructions, including the barcode label, consent form and return envelope.
Only a small sample is needed. Use the supplied stick, close the tube as instructed and return it promptly. For a kit from another service, follow that service’s collection and return instructions.
You do not usually need to change what you eat for FIT. Continue prescribed medicines, including blood thinners, unless the clinician arranging the test specifically advises otherwise.
Private or self-funded bowel screening kits
You can buy a bowel screening kit privately, including if you are outside the public screening age range. Before buying one, discuss your age, symptoms, family history and any previous polyps with your GP. These help determine whether a stool test or another investigation is appropriate.
Not all commercial kits are FIT. Some look for blood, while others look for DNA changes in cells shed into the poo. They have different evidence and limitations. The FIT figures on this page cannot be applied to every commercial test, and paying for a kit does not make it a complete check of your bowel.
What should I check before buying?
- What does the test measure, and how well does it detect cancer and precancerous polyps separately?
- Who reviews the result, and will a copy be sent to your GP?
- Who arranges follow-up if the result is positive or the sample cannot be processed?
- What does the price include? A consultation or colonoscopy may cost extra. Check any insurance cover directly with your insurer.
What happens after a private result?
Share the full report with me or your GP, including the test name and any numerical result. A positive result needs prompt medical review. Do not use a later negative home test to dismiss an earlier positive result.
A positive private test does not by itself guarantee a publicly funded colonoscopy. Public referral criteria and your clinical circumstances determine access. Your GP can advise on the available options. Buying a private kit does not enrol you in the National Bowel Screening Programme.
If you have bowel symptoms or a colonoscopy has already been recommended, speak to me or your GP. A negative private test should not delay that assessment or replace the recommended colonoscopy.
Common questions
Why do screening and symptom tests use different cut-offs?
The cut-off is the amount of blood that counts as a positive result in that pathway. A lower cut-off may be used when checking symptoms than in routine screening. Results can also be reported in different units. The correct pathway and laboratory units are needed to interpret the number. It is not a percentage chance of cancer.
What if I have piles or visible blood?
Piles can bleed, but should not automatically be assumed to explain a positive FIT. If you see blood in your poo, let me or your GP know. Do not postpone assessment while waiting for a screening kit. If a FIT was arranged to investigate symptoms, follow the advice from that service about completing it.
What if I am having my period?
Menstrual blood can contaminate a sample. Wait until your period has finished before collecting it, and follow any additional timing advice in your kit. If you are unsure, contact the service that arranged the test. Let them know if the sample may have been contaminated.
Can FIT replace polyp surveillance?
A negative FIT does not replace your recommended follow-up colonoscopy. The recommended interval will be documented in your endoscopy report and/or histology report once the tissue results are available.
Ongoing symptoms need review, even after a negative FIT
Contact me or your GP if bowel symptoms persist, come back or get worse. If they have already lasted six weeks or longer, arrange a review now. Seek advice sooner for new or persistent bleeding, unexplained weight loss or worsening symptoms.
When I assess your symptoms, I consider the FIT result alongside your history, examination and blood tests. Iron deficiency anaemia (a low blood count caused by low iron) may need further investigation despite a negative FIT.
When to get urgent help
Seek urgent medical help for heavy or ongoing bleeding, black tarry stools, severe abdominal pain, or feeling faint or very unwell.
Call 111 for an ambulance if you collapse, have heavy bleeding with faintness, or are too unwell to travel safely. Do not wait for a routine appointment or an email reply.
Three things to remember
- FIT detects blood. It does not look directly at the bowel or diagnose cancer.
- Some precancerous polyps do not bleed. A negative FIT cannot confirm that the bowel is free of polyps or cancer.
- Colonoscopy can find and remove polyps and take biopsies. A negative FIT does not replace a recommended colonoscopy.
Related patient information
Sources and further reading
Main clinical evidence reviewed 14 October 2026. Local screening eligibility, international comparisons and pathway context checked 15 October 2026. Your own symptoms and results determine the advice for your care.
- Health NZ: current bowel screening eligibility
- Health NZ: FIT when assessing bowel symptoms
- Health NZ: lower bowel investigation guidance (2026)
- HealthEd: NZBSP test kit instructions
- Health NZ: doing the bowel screening test
- 2024 screening study: FIT detection of advanced precancerous lesions
- 2019 systematic review: FIT accuracy varies by cut-off
- National Cancer Institute: stool tests and colonoscopy
- Health NZ: colonoscopy and its safety
- Bowel Cancer NZ: public and private screening options
- Australian Government: How bowel screening with the program works
- NHS: Bowel cancer screening
- USPSTF: Colorectal Cancer Screening final recommendation