The symptoms that need a GP, not a home test.

This is the least commercial thing on this website, and the most important. If you have any of the symptoms below, do not buy a screening test. Book a GP appointment.

The five that matter

• Bleeding from the back passage, or blood in your stool. Bright red or dark, mixed in or on the paper. Piles are a common cause, and piles are not a reason to skip the appointment.
• A change in bowel habit lasting three weeks or more. Looser, more frequent, or new constipation. The key word is persistent: a few unsettled days after a takeaway is not this.
• Weight loss you cannot explain. Weight coming off without a change in diet or exercise.
• Abdominal pain, discomfort or bloating that keeps coming back, particularly if it is worse after eating or is putting you off food.
• Tiredness that is new and unexplained, especially alongside any of the above. Slow bleeding from the bowel causes iron deficiency anaemia long before anyone notices blood.

Why a screening test is the wrong answer here

Screening looks for disease in people who have no reason to suspect it. The maths only works in a population who feel well. Once you have a symptom, your individual risk is higher than the population risk the test was designed around, and two things follow.

First, no stool test rules cancer out. A normal result lowers the probability, it does not eliminate it. Second, and this is the real danger, a normal result is reassuring. People who get one tend to wait. Waiting is exactly what you cannot afford when the symptom is the thing that would have got you referred.

Bowel cancer caught at stage one has an excellent outlook. Caught at stage four it does not. The difference is very often nothing more than how quickly someone acted on a symptom.

What your GP will actually do

Expect questions about the pattern and duration of the symptom, an examination that may include an examination of the back passage, and blood tests to check for anaemia. Your GP will probably ask you to do a FIT test, which measures blood in the stool and is used to decide how urgently you need to be seen.

If the picture suggests it, you will be referred on an urgent suspected cancer pathway, which in England means being seen within two weeks. That referral is free, faster than anything you can buy privately, and leads to colonoscopy where it is needed. Colonoscopy sees the bowel directly and can remove a polyp during the same procedure. No stool test, ours included, does that.

The awkward part

Most people who present with these symptoms do not have cancer. Haemorrhoids, irritable bowel syndrome, diverticular disease and simple dietary change account for the large majority. That is a good reason to go, not a reason to stay at home: you will probably be reassured, and if you are not, you will have found it early.

Embarrassment is the other reason people wait. GPs see this every single day. It is a five-minute conversation, and the alternative is worse.

When screening is right

If you feel well, have no symptoms and want to check, that is what screening is for. Take part in the NHS programme when you are invited. If you are outside the invited age range or want to test between rounds, a private test is a reasonable addition — but it sits alongside the NHS programme, never instead of it, and never instead of seeing a doctor about a symptom.

If bleeding is heavy, or you have severe abdominal pain, persistent vomiting or you feel faint, call 111, or 999 if it is severe.