What Is the FOBT?
The FOBT — short for faecal occult blood test, or more precisely the immunochemical FOBT (iFOBT) — is a home test that checks your stool for blood you cannot see with the naked eye. "Occult" simply means hidden. It is the test at the heart of Australia's National Bowel Cancer Screening Program.
The test kit is posted to your home every two years if you are aged 45 to 74. You collect small samples from two separate bowel motions, seal them in the provided packaging, and return them by post to the laboratory. You do not need to change your diet or stop any medications — the current test only detects human blood and is not affected by what you eat.
The test is completely free through the National Program and takes only a few minutes. Sadly, less than half of eligible Australians complete it each time — which means many treatable cancers and precancerous growths are being missed. You have already done the most important part by completing yours.
What Does a Positive Result Actually Mean?
A positive FOBT means the laboratory found traces of human blood in your stool sample. It does not mean you have cancer. It means something is causing a small amount of bleeding somewhere in your digestive tract, and we need to find out what.
Most of the time, a positive FOBT turns out to have a benign explanation. Common causes include:
- Haemorrhoids (piles) — swollen blood vessels near the back passage that bleed during bowel motions
- Anal fissure — a small tear in the lining of the back passage
- Diverticular disease — small pouches that form in the wall of the bowel, which can bleed
- Bowel polyps — small growths on the bowel lining that may bleed slowly and can be precancerous
- Colorectal cancer — tumours in the colon or rectum that bleed into the bowel
- Stomach ulcers or irritation — bleeding from higher up in the gut can occasionally show up on this test
It is also possible — though uncommon — to get a positive result that turns out not to have a significant cause. Some medications (like ibuprofen, aspirin, or blood thinners) can cause minor GI bleeding. But even then, the result cannot be assumed harmless without looking properly. A colonoscopy is always needed.
Why You Always Need a Colonoscopy After a Positive FOBT
This is important: all positive FOBT results require a colonoscopy, regardless of how you feel and regardless of whether you think haemorrhoids are the likely explanation.
Here is why that rule exists: roughly 1 in 25 people with a positive FOBT will be found to have colorectal cancer on colonoscopy. And roughly 1 in 5 will have significant precancerous polyps that need to be removed before they become cancerous. Both of those numbers are far higher than in the general population — this is exactly how the screening programme is designed to work.
Critically, haemorrhoids and bowel cancer can both be present at the same time. Assuming a positive FOBT is "just haemorrhoids" without a colonoscopy is one of the most common reasons bowel cancer is diagnosed late. A colonoscopy is the only test that lets your specialist look directly at the entire bowel lining.
Please do not put this off, even if you feel completely well. Bowel cancer — particularly in the right side of the colon — can bleed silently for months without causing any noticeable symptoms. Follow-up colonoscopy is always required, no matter how good you feel.
What Happens After a Positive FOBT — Step by Step
You receive your positive result by mail from the National Bowel Cancer Screening Program. A letter will encourage you to see your GP promptly. Do not wait.
See your GP as soon as possible. Your GP will go through your result with you, ask about any symptoms, review your medications and family history, and decide how urgently the colonoscopy referral needs to happen.
Your GP refers you to a colorectal surgeon. If you have symptoms — rectal bleeding, a change in bowel habit, unexplained weight loss, or abdominal pain — the referral should be urgent. If you have no symptoms, it is still important and should be arranged promptly.
Your colonoscopy is arranged. You will be given instructions for bowel preparation — a laxative solution taken at home the day before. The colonoscopy itself is done under sedation and usually takes 20–40 minutes. Any polyps found can almost always be removed at the same time.
Results and follow-up. Your specialist will talk through what was found when you wake up. A written report follows within a few days. Depending on what was found, you will either receive reassurance, a follow-up schedule, or — if something more serious is detected — a referral for further assessment.
What Is the Colonoscopy Likely to Find?
Most people who have a colonoscopy after a positive FOBT receive reassuring news. Here is what the results typically look like:
- Normal bowel — around 50–60% of colonoscopies after a positive FOBT find nothing significant. This is a genuinely good outcome — the test did its job, and your bowel looks clear.
- Polyps — some people have growths called adenomas (pre-cancerous polyps) or smaller, lower-risk polyps called hyperplastic polyps. These are removed during the colonoscopy via a procedure called a polypectomy. The type and number of polyps found determines how soon you need a follow-up colonoscopy.
- Bowel cancer — found in about 4% of people with a positive FOBT. If cancer is detected, you will be referred promptly for CT scans to check staging, and a specialist team will put together a treatment plan with you.
- Other benign findings — such as diverticular disease (small pouches in the bowel wall) or haemorrhoids.
The reason screening matters so much is the difference early detection makes. Bowel cancer caught at Stage I — before it has spread — has a five-year survival rate of over 90%. Caught at Stage IV, that figure drops dramatically. Completing your screening and following up a positive result is one of the most significant things you can do for your health.
What If the Colonoscopy Finds Nothing?
A positive FOBT followed by a normal or benign colonoscopy is not a wasted experience — it is a reassuring one. The test flagged a possible concern; the colonoscopy confirmed nothing serious is happening. That is screening working exactly as it should.
It is worth knowing that some things can cause a positive FOBT without significant underlying pathology:
- Anti-inflammatory pain medications (aspirin, ibuprofen, naproxen) — these can cause microscopic bleeding in the stomach
- Blood thinners (warfarin, rivaroxaban, apixaban) — increase bleeding tendency throughout the gut
- Haemorrhoids or anal fissures — minor bleeding from these benign conditions
- Heavy exercise — occasionally causes trace gut bleeding
- Sample contamination with menstrual blood
Even knowing these factors, the colonoscopy is still necessary — none of them can be assumed to be the full explanation without looking properly.
About the National Bowel Cancer Screening Program
Australia's National Bowel Cancer Screening Program is one of the best in the world. It sends a free home testing kit every two years to all Australians aged 45 to 74, linked automatically to your Medicare enrolment. The starting age was recently lowered from 50 to 45, in part because bowel cancer rates in younger adults have been rising.
A few important points to know:
- The kit and pathology testing are completely free — there is no cost to you
- No dietary restrictions are needed for the current test
- If you have not received a kit but are in the eligible age range, you can request one by calling 1800 627 701 or visiting cancerscreening.gov.au
- The programme reduces bowel cancer deaths — but only when participants act on positive results
If you have a personal history of bowel cancer or polyps, or a strong family history of the disease, you may be better served by colonoscopy directly rather than FOBT screening. Your GP can advise on what is right for your situation.
What to Do Right Now
If you have received a positive FOBT and have not yet seen your GP, please book an appointment as soon as possible. Do not wait for symptoms to appear — the whole point of screening is to catch things before symptoms develop.
If your GP has already referred you for a colonoscopy, our rooms can arrange an appointment promptly. We aim to see most patients within 1–2 weeks of referral. If you have symptoms alongside the positive result — significant rectal bleeding, unexplained weight loss, or a noticeable change in your bowel habits — let us know so we can arrange a priority appointment.
It helps to come to your first appointment with:
- Your FOBT result letter from the National Program
- Any recent blood test results (particularly iron levels or a full blood count)
- A list of your current medications
- Details of any bowel symptoms you have noticed
- Any family history of bowel cancer or polyps
Frequently Asked Questions
Yes. Feeling well is not the same as having a clear bowel. Bowel cancer and significant polyps often cause no symptoms at all — especially in the early stages when they are most treatable. The whole reason we screen before symptoms appear is because by the time you feel unwell, the cancer may already be at a more advanced stage. Please do not let feeling fine be a reason to delay this.
It is possible — haemorrhoids are very common in the age group targeted by screening. But haemorrhoids and bowel cancer can exist at the same time, which is why haemorrhoids alone cannot explain away a positive FOBT. A colonoscopy will check your entire bowel and tell you definitively what is going on.
About 1 in 25 people with a positive FOBT will be found to have bowel cancer on colonoscopy — that is 4%. About 1 in 5 will have significant precancerous polyps. The majority — roughly half — will have a completely normal colonoscopy. So the odds are actually in your favour, but the stakes are high enough that you should not skip the investigation.
If you also have symptoms — visible blood, a change in your bowel habits, weight loss, or abdominal pain — the referral should be treated urgently and colonoscopy arranged within weeks. If you have no symptoms, it should still happen promptly — ideally within 1–3 months of your positive result. Delays are a known cause of late-stage diagnoses.
No. Most polyps — even the precancerous type called adenomas — are not cancer. They are simply growths that could become cancerous over years if left alone. Removing them during the colonoscopy is a straightforward, safe procedure called a polypectomy. Finding and removing polyps before they turn into cancer is one of the most important things colonoscopy can do for you.
The FOBT is not a perfect test. Some cancers and polyps only bleed intermittently — they may not have been bleeding at the exact time of your previous test. A positive result now simply means something may have changed, or the source was not detectable then. A positive result at any testing cycle always requires follow-up. Your previous negative result does not cancel this one out.
Learn more about what happens during a colonoscopy — including preparation, what to expect on the day, and recovery.
Procedure details →Received a positive FOBT? Please do not put it off.
Contact our rooms on (03) 9816 3951 or ask your GP for a referral to Mr Nguyen at North Eastern Surgical. Send an enquiry →