Positive Faecal Occult Blood Test: What It Means
Medically Reviewed by Dr. Pedro Yelamo Vera, MD
Licensed Physician No. 484814280 · Official Medical College of Bizkaia (Spain)Last reviewed: 5 November 2026
A positive faecal occult blood test is not a diagnosis.
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A positive faecal occult blood test means blood was found in your poo that you cannot see. It is not a cancer diagnosis: the cause is often piles, a small tear or polyps. But it always needs to be looked into, nearly always with a colonoscopy, and you should not just repeat the test instead. This guide is by Dr. Pedro Yelamo Vera, a GP licensed in Spain (Colegiado No. 484814280).
- The test looks for hidden traces of blood in the stool.
- A positive result is not a diagnosis. Most people with a positive test do not have cancer.
- Common causes are piles, a tear, polyps, diverticula or bowel inflammation.
- The usual next step is a colonoscopy. Do not repeat the test to "check".
- In Spain, bowel screening is offered from 50 to 74, every 2 years. England uses the same ages.
- Black stools, a lot of blood or feeling faint on standing are an emergency: call 112.
What is a faecal occult blood test?
It is a test of a small poo sample that you collect at home with a kit. It looks for blood you cannot see. The blood can come from anywhere in the gut. It is used mainly to find bowel cancer before it causes symptoms, and also to look for the cause of anaemia.
There are two types. The FIT test (faecal immunochemical test) picks up human blood and needs no diet. It is the one used in screening. The older guaiac test may mean avoiding some foods and medicines first. In Spain it is called sangre oculta en heces (SOH), and the FIT is the test inmunológico. In the US it is spelt fecal occult blood test (FOBT).
What does a positive result mean?
It means there was blood in the sample. It does not say where it came from or why. As MedlinePlus puts it, the test cannot diagnose any disease on its own. The most common causes are:
- Piles (haemorrhoids) or a small tear in the anus (fissure).
- Bowel polyps. Most are not cancer, though some can turn into cancer over years.
- Diverticula, small pouches in the bowel wall.
- Bowel inflammation, such as ulcerative colitis or Crohn's disease.
- Ulcers or sore patches.
- Bowel cancer, in a small number of cases.
What happens after a positive test?
The usual next step is a colonoscopy. A thin tube with a camera looks inside the bowel. It shows where the bleeding comes from, and polyps can be removed at the same time. If the test was part of a screening programme, the programme usually books it for you. If you did the test yourself, see your doctor so they can request it.
Do not repeat the test hoping for a negative. A later negative does not cancel the positive, because bleeding can come and go.
Can it be a false positive?
Yes. Piles, a fissure, a period or bleeding gums can all cause a positive. With the guaiac test, some foods or medicines can too. Even so, a doctor cannot tell if it is a false positive without looking. That is why a colonoscopy is done.
How does bowel screening work in Spain, the UK and the US?
Spain: the Ministry of Health says screening is offered to men and women aged 50 to 74, with a stool test every 2 years. Each region runs its own programme and sends the invitation. People with a strong family history or bowel inflammation follow a different plan set by their doctor.
England: the NHS invites people aged 50 to 74 every 2 years with a home FIT kit. If blood is found, you see a specialist nurse and usually have a colonoscopy.
US: screening usually starts at 45, and a stool test is repeated more often than in Europe, often every year.
If you see blood in your poo, do not wait for screening: see a doctor. Read also what your stool colour means.
Does a negative test mean I am fine?
A negative result is good news, but it does not rule everything out. If you have symptoms, see a doctor anyway:
- Blood in your poo, or black poo.
- A change in bowel habit that lasts more than 3 weeks.
- Weight loss you cannot explain.
- Tiredness from anaemia.
- Tummy pain that does not go away.
When should I call 112?
- Black, tar-like poo or a lot of red blood.
- Feeling dizzy, fainting or looking very pale.
- Vomiting blood or what looks like coffee grounds.
- Sudden, severe tummy pain.
If you have any of these, call 112 or go to A&E (urgencias).
Frequently asked questions about the faecal occult blood test
Does a positive result mean I have cancer?
No. Most people with a positive test do not have cancer. But the cause has to be found, nearly always with a colonoscopy.
Can piles cause a positive test?
Yes. Even so, a doctor cannot put it down to piles without checking the bowel.
Do I need a special diet before the test?
Not for the FIT test used in screening. The guaiac test sometimes needs one. Follow the kit's instructions.
Can I do the test during my period?
It is better to wait a few days after your period so the sample is not mixed with blood. Follow your programme's instructions.
Can a doctor go through my result by video?
Yes. A doctor can explain the report, ask about symptoms and guide the next steps, such as a colonoscopy.
Getting a medical assessment
If you are in Spain and you have a positive result that worries you, you can book a video consultation with Dr. Pedro Yelamo Vera, a physician registered in Spain. You can also read about tummy pain, piles and understanding test results. A prescription is never guaranteed: it is issued only where clinically appropriate after a genuine evaluation, as a private electronic prescription under Spanish law. This service is for urgent, non-emergency care. In an emergency, call 112.
This guide is general information. It does not replace the package leaflet or the advice of your doctor or pharmacist.
Sources
This content is written and reviewed by a licensed physician with reference to the following sources.
