Bowel cancer and the FIT test: two tests with the same name

Clinical Rounds, the GPAtlas podcast. Malignancy & Cancer. 18 minutes. Published 31 August 2026. Free to listen.

Clinical source: our own Ocean article "Lower Gastrointestinal (GI) Cancers (Colorectal and Anal Cancers)", last reviewed 25 May 2026.

Transcript

Sarah: Hello, and welcome to GPAtlas Clinical Rounds. I'm Sarah, and this is the podcast where we take one thing you'll genuinely see this week and work out what to do with it.

Ben: And I'm Ben. Today, bowel cancer, and one specific piece of reassurance that isn't reassuring at all.

Sarah: Mrs Ferreira is sixty-three. She's noticed her bowels have been looser for a couple of months, and there's been a bit of blood, which she's put down to piles because she's had them for years. And then she says the sentence that makes the whole consultation, which is, and I did that kit they sent me, it was fine, so I wasn't going to bother you.

Ben: Three things. Why the kit she did and the test you're about to order are not the same test. Who gets a FIT, which is broader than most people think. And what a negative result actually licenses you to do, which is less than most people think.

Sarah: So, the two tests. She's had a screening FIT, through the national programme, and she's about to have a symptomatic FIT, ordered by me. Same technology, same kit in her hand, completely different question being asked.

Ben: And the difference is the threshold, which is where the danger sits. Our article says the screening FIT threshold, a hundred and twenty micrograms of haemoglobin per gram in England, now being lowered towards eighty, is far higher than the symptomatic referral threshold of ten or above. So a screening test can come back normal at a hundred and nineteen, and that same result, in a symptomatic patient, is more than ten times the referral threshold.

Sarah: Which is why our article says explicitly to offer a symptomatic FIT even if a recent screening FIT was negative. Her clean screening result is not evidence about her symptoms. It was answering a different question with a much blunter threshold, and she has no way of knowing that. Neither, honestly, do a lot of us.

Ben: A hundred and twenty is normal for screening. Ten is the referral threshold.

Sarah: And it's worth saying what screening is for, so you can explain it. The programme posts a two-yearly home kit to everyone aged fifty to seventy-four in England, and the rollout to fifty-year-olds finished in twenty twenty-five. Over seventy-fives can request a kit through the helpline. And the key line: screening is for asymptomatic people only.

Ben: Which means the moment she developed symptoms she left the screening population. She's not a screened person who's fine. She's a symptomatic patient who happens to have done a screening test, and those are different clinical objects.

Sarah: Symptoms take her out of the screening population entirely.

Ben: So who gets a symptomatic FIT. Our article gives the list and it's worth having in your head because it's broader than the old two-week-wait criteria. Offer FIT for an abdominal mass, a change in bowel habit, or iron-deficiency anaemia, at any age. Forty or over with weight loss and abdominal pain. Under fifty with rectal bleeding plus abdominal pain or weight loss. Fifty or over with rectal bleeding, abdominal pain or weight loss. And sixty or over with anaemia even without iron deficiency.

Sarah: That last one catches people. Sixty or over with anaemia, and it doesn't have to be iron deficient. The reflex is to look at the ferritin, see it's normal, and file it as anaemia of chronic disease. In the over-sixties that's still a FIT.

Ben: And three findings bypass FIT completely and go straight to referral: a rectal mass, an unexplained anal mass, or unexplained anal ulceration. If you can feel it, you don't test for blood in the stool, you refer.

Sarah: Which means the rectal examination isn't optional. Our article calls it essential, to assess for a low rectal or anal mass and to inspect the perianal skin. And then adds the caveat that keeps you honest: a normal rectal examination does not exclude a more proximal lesion. So you have to do it, and it can't reassure you if it's normal.

Ben: If you can feel it, refer. Do not test it.

Sarah: Now the trap that has Mrs Ferreira's name on it, which is her piles. She's had haemorrhoids for years, she's got blood, and the arithmetic feels obvious. Our article's line is the one to remember: young-onset colorectal cancer is rising, and visible perianal haemorrhoids do not exclude a proximal tumour.

Ben: Seeing haemorrhoids doesn't mean they're the source. Most people over fifty have some. Finding them tells you almost nothing about where the blood came from, and the temptation to stop looking once you've found a benign explanation is exactly what makes a delayed diagnosis.

Sarah: And the timing detail that helps in the history: a change in bowel habit of six weeks or more is significant. So the question isn't have your bowels changed, it's when did they change. Two weeks is a different conversation to two months, and patients rarely volunteer the duration unless you ask for it directly.

Ben: Haemorrhoids do not exclude a tumour higher up.

Sarah: So her FIT comes back at six. Under ten. What does that let me do? And the honest answer, from our own article, is less than I'd like. A result below ten lowers but does not remove the risk of cancer.

Ben: And then the sentence that should govern the follow-up: a low FIT is not a discharge. Keep symptomatic patients under active review, safety-net explicitly, and refer regardless of the FIT result if clinical concern is strong or a sample is not returned. So the test triages. It doesn't discharge.

Sarah: And the unreturned sample, which is a real-world problem rather than a clinical one. Our article says not to delay referral for strong clinical concern, for example an abdominal mass, even if the FIT is below ten or a sample is never returned. So the referral cannot be held hostage to a kit sitting in somebody's bathroom.

Ben: It also says to provide support to return the sample where needed, and to arrange extra help for people who need it. Which sounds like an administrative footnote and isn't. The patients least likely to return a kit are often the ones you're most worried about.

Sarah: A low FIT is not a discharge. It is a triage result.

Ben: Two things about the test itself that are worth knowing because patients ask. It's immunochemical, so it detects human haemoglobin specifically. That means no dietary restriction is needed, and oral iron or animal blood in the diet don't cause false positives, unlike the old guaiac test. Iron darkens the stool and can mimic melaena, but it doesn't affect the FIT.

Sarah: Which matters practically, because if she's anaemic you'll want to start iron, and you don't have to sequence that around the test. Start the iron, send the FIT.

Ben: And on the iron, a dosing point that's changed and hasn't reached everybody: one tablet once daily is as effective as higher or divided doses, and it's better tolerated. Continue for about three months after the haemoglobin normalises to replenish the stores. And unexplained iron-deficiency anaemia warrants assessment of both the upper and lower gastrointestinal tract, not just the bowel.

Sarah: With one safety point our article includes that I'd forgotten: iron overdose is a leading cause of fatal childhood poisoning, so it's stored out of reach. And separate the doses from levothyroxine, bisphosphonates, tetracyclines and quinolones, because absorption drops.

Ben: Once daily beats divided doses. And iron does not affect the FIT.

Sarah: Two more that change the urgency completely. Signs of bowel obstruction, so vomiting, marked distension, absolute constipation, colicky pain, is a same-day acute surgical admission. That's not a cancer pathway, that's today.

Ben: And a marker that's easy to walk past on a full blood count: thrombocytosis, a raised platelet count, is itself a recognised marker of possible underlying cancer. So a raised platelet count in someone with vague abdominal symptoms is a finding, not an incidental.

Sarah: And on the referral itself, the administrative bit that decides whether any of this works. Make suspected cancer pathway referrals within one working day, say clearly whether it's urgent, use the local proforma. The Faster Diagnosis Standard aims for diagnosis or exclusion within twenty-eight days, and that clock starts when you send it, not when you decide to.

Ben: Raised platelets is a finding. Not an incidental.

Sarah: I want to come back to what Mrs Ferreira said, because I think it's the most important sentence in the episode and it isn't a clinical one. She said, I did that kit they sent me, it was fine, so I wasn't going to bother you. There are three separate problems packed into that. She thinks the kit answered her question. She thinks a normal result means don't come. And she's apologising for being there at all.

Sarah: And the second one is the dangerous one, because it's a delay we've built ourselves. We send people a test, they get a normal result, and quite reasonably they file it as bowel checked, all clear, for the next two years. Nobody tells them that a negative kit and a new symptom are completely unrelated facts. So the screening programme, which saves lives, also generates a specific kind of false reassurance in exactly the people who then develop symptoms.

Sarah: So the thing I've started saying, in about one sentence, is that the kit checks people with no symptoms, and once you've got symptoms we do a different, much more sensitive version of the same test. That's it. It takes ten seconds, it explains why I'm re-testing something she thinks was already done, and it means the next time she notices something she rings us instead of waiting for the post.

Ben: And it protects the referral too. Because if she doesn't understand why she's being tested again, she may not return the sample, and an unreturned sample is one of the ways this pathway fails quietly. Our article's answer to that is to refer anyway where clinical concern is strong, but the better outcome is that she posts it.

Sarah: And the last piece is the safety-net, worded for someone who's just been told her test was fine. Our article gives a patient-facing line I like: please return the sample even if it feels awkward, because finding any problem early gives the best chance of simple, successful treatment. And then the clinical half of it, which is that if the symptoms carry on or get worse she comes back regardless of the number, because a low result lowers the risk without removing it.

Ben: She thinks the kit answered her question. Ten seconds fixes that.

Ben: One more thing worth being precise about, because it's where the two thresholds cause real-world confusion. When you order a symptomatic FIT, the lab is running the same assay it runs for screening. What differs is the number you act on.

Ben: So a patient can genuinely be told their screening test was negative and then be told, weeks later, that their FIT is positive, on the same technology and possibly a similar underlying value. That sounds to them like one of the two tests was wrong, or that something has changed fast, and neither is true.

Ben: Which is worth pre-empting when you order it, in a sentence. This is the same test, but because you have symptoms we act on a much lower level than the screening programme does. That stops the result landing as a contradiction, and it stops the phone call where she asks which test to believe.

Sarah: Same assay. Different number. Say so when you order it.

Sarah: And one thing about who returns these kits, which our article flags twice and which I think is the quiet inequality in this pathway. It says to provide support to return the sample where needed, and to arrange extra help for people who need it.

Sarah: Because returning a stool sample by post requires a level of confidence, literacy and organisation that we tend to assume. And the patients least likely to manage it, older, frailer, less confident, non-English-speaking, are not a random subset. If the pathway quietly depends on a kit coming back, it will work best for the people who needed it least.

Ben: An unreturned kit is not a neutral event. It has a pattern.

Ben: Exam corner. A sixty-three year old woman reports two months of looser stools and intermittent rectal bleeding. She has known haemorrhoids, and her NHS bowel screening FIT four months ago was negative. Examination reveals external haemorrhoids and a normal rectal examination. What is the most appropriate next step? A, reassure her, given the negative screening FIT. B, treat the haemorrhoids and review in six weeks. C, arrange a symptomatic FIT and safety-net. Or D, refer urgently without any further testing.

Ben: It's C. She has a change in bowel habit lasting more than six weeks, which is an indication for a symptomatic FIT at any age, and our article says to offer one even after a negative screening FIT, because the screening threshold is far higher. A is the central error of this episode. B is wrong because visible haemorrhoids do not exclude a proximal tumour. D isn't unreasonable clinically, but she has no rectal mass, anal mass or anal ulceration, and those are the three findings that bypass FIT, so the pathway here is to test and refer on the result, while safety-netting regardless.

Sarah: So. Three things for Monday. One. A negative screening kit says nothing about symptoms, because the thresholds are a hundred and twenty versus ten. Two. Sixty or over with anaemia gets a FIT even if it isn't iron deficient. And three. A low FIT is not a discharge, so the safety-net and the review have to be as explicit as if you'd found nothing at all.

Sarah: One thing to reflect on, if you're logging this. Think about how many times you've heard a patient say their screening test was fine. Did you check what that test was actually measuring? The full transcript and the references are on the episode page. Ben and I are synthetic voices. The medicine isn't. See you next week.

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