What screening is
Screening means offering a test to a group of people who have no symptoms, to find a cancer early or to find changes that could become cancer. Some screening, such as cervical and bowel screening, can prevent cancer by finding and treating those changes.
Screening programmes are designed for populations, based on evidence about who benefits most. That is why ages and intervals are set, and why they differ between countries.
Screening vs diagnostic testing
Screening
- For people who feel well
- Offered at set ages and intervals
- Looks for early signs across a population
- A positive result leads to diagnostic tests
Diagnostic testing
- For people with symptoms or an abnormal result
- Arranged at any age when needed
- Looks for the cause of a specific problem
- Often involves imaging and a
Common screening tests
Country examples show how programmes differ. They are illustrations, not advice. Check your local programme.
Breast screening
Looks for breast cancer in people without symptoms, usually with a mammogram every two or three years.
Test: Mammogram (breast X-ray). Some programmes use clinical breast examination.
Who it is for: Women and some trans and non-binary people within age ranges set by each programme. People at higher risk because of family history or an inherited gene change may be offered earlier or extra screening.
Possible benefits
- Can find cancers early, when treatment is often simpler and more effective
- Regular screening lowers the risk of dying from breast cancer in the age groups studied
Limitations
- Some cancers are missed, especially in dense breasts
- Recalls for extra tests are common and most turn out not to be cancer
- Some cancers found would never have caused harm (overdiagnosis)
How programmes differ (examples, not advice)
- United States: USPSTF (2024): a mammogram every two years from age 40 to 74 for women at average risk. Source
- England: NHS: invitations every three years from age 50 to 71. Source
- India: The national programme for non-communicable diseases includes clinical breast examination for women aged 30 and over at primary-care level; availability varies by state. Source
How to prepare
- Wear a two-piece outfit
- Avoid deodorant or talc on the day if you can
- Tell staff about implants, previous surgery or tenderness
If the result is abnormal
Being called back usually means the images need a closer look. Most people who are recalled do not have cancer. Next steps can include more images, an ultrasound or a biopsy.
Cervical screening
Finds high-risk HPV and cell changes early, so they can be treated before cancer develops.
Test: HPV test (increasingly self-collected), sometimes with a Pap smear. Some programmes use visual inspection with acetic acid (VIA).
Who it is for: Women and people with a cervix within programme ages. Vaccinated people still need screening.
Possible benefits
- One of the most effective screening programmes: it can prevent cancer, not only find it early
- Self-sampling makes screening easier for many people
Limitations
- A positive HPV result is common and usually clears on its own
- Screening does not look for ovarian or womb cancer
How programmes differ (examples, not advice)
- World Health Organization: WHO recommends HPV DNA testing as the main screening method, starting at age 30 and repeating every 5 to 10 years. Women living with HIV start at 25 and are screened more often. Source
- England: NHS: ages 25 to 64. Since July 2025, people aged 25 to 49 who test HPV-negative are invited every five years. Source
- India: The national programme includes cervical screening, often by VIA, for women aged 30 and over; HPV testing is expanding. Source
How to prepare
- Book outside your period if you can
- You can ask for a female clinician, a chaperone or a smaller speculum
- Ask whether self-sampling is available
If the result is abnormal
An abnormal result usually means HPV or cell changes, not cancer. You may be asked to repeat the test or have a colposcopy, a closer look at the cervix.
Bowel (colorectal) screening
Finds hidden blood or polyps so bowel cancer can be prevented or found early.
Test: Stool test (FIT) at home, or colonoscopy in some countries.
Who it is for: Adults in middle and older age, within ages set by each programme. People with a strong family history may start earlier.
Possible benefits
- Removing polyps can prevent cancer
- Home stool tests are private and simple
Limitations
- A positive stool test often has a harmless cause, such as piles
- Colonoscopy carries a small risk of bleeding or a tear
How programmes differ (examples, not advice)
- United States: USPSTF (2021): screening from age 45 to 75, with a choice of stool tests or colonoscopy. Source
- England: NHS: a home FIT kit every two years from age 50 to 74. Source
How to prepare
- Follow the kit instructions carefully and post it promptly
- For colonoscopy, follow the bowel preparation instructions and arrange a lift home if sedated
If the result is abnormal
A positive FIT means blood was found, not that you have cancer. The usual next step is a colonoscopy.
Lung screening
A low-dose CT scan for people at high risk because of their smoking history.
Test: Low-dose CT scan.
Who it is for: Usually adults with a significant smoking history, in specific age ranges. Not offered to everyone.
Possible benefits
- In the large US National Lung Screening Trial, low-dose CT reduced lung cancer deaths by about 20% compared with chest X-ray in heavy smokers
Limitations
- Findings that turn out to be harmless are common and can lead to more scans
- Small radiation dose each year
- Screening does not replace stopping smoking
How programmes differ (examples, not advice)
- United States: USPSTF (2021): a yearly low-dose CT from age 50 to 80 for people with a 20 pack-year smoking history who smoke now or quit within the past 15 years. Source
- England: NHS lung cancer screening is being rolled out for people aged 55 to 74 who have ever smoked. Source
How to prepare
- Bring details of your smoking history
- Ask about stop-smoking support at the same visit
If the result is abnormal
Many scans show small nodules. Most are not cancer and are checked again with a later scan.
Prostate (PSA) testing
A blood test that is not a routine screening test in many countries: it is an individual decision after talking through benefits and harms.
Test: PSA blood test, sometimes followed by MRI.
Who it is for: Men and people with a prostate, usually from middle age. Those with a family history or of Black African or Caribbean ancestry may be at higher risk and should ask about it earlier.
Possible benefits
- May find some prostate cancers earlier
- MRI before biopsy has reduced unnecessary biopsies in many places
Limitations
- PSA can be raised by an enlarged prostate, infection or recent activity
- Can find slow-growing cancers that would never cause harm, leading to overtreatment
How programmes differ (examples, not advice)
- United States: USPSTF (2018): for ages 55 to 69, an individual decision after discussing benefits and harms. An update is in progress. Source
- United Kingdom: The UK National Screening Committee consulted on a draft recommendation in late 2025. Check the current position. Source
How to prepare
- Avoid ejaculation and vigorous cycling for about 48 hours before the test
- Ask for a decision aid to weigh up the pros and cons
If the result is abnormal
A raised PSA does not mean cancer. Next steps may include a repeat test, an MRI and sometimes a biopsy.
Oral (mouth) screening
A quick look inside the mouth for patches or ulcers, most useful for people who use tobacco, betel quid or alcohol.
Test: Visual examination of the mouth by a trained health worker or dentist.
Who it is for: Offered as part of some national programmes, particularly where tobacco chewing is common; dentists often check during routine visits.
Possible benefits
- Painless and quick
- Can find pre-cancerous patches that can be treated
Limitations
- Depends on the training of the examiner
- Not a substitute for seeing someone about a lasting symptom
How programmes differ (examples, not advice)
- India: The national programme includes oral visual examination for adults aged 30 and over at primary-care level. Source
How to prepare
- Remove dentures if asked
- Mention any patch or ulcer that has lasted more than three weeks
If the result is abnormal
A suspicious patch is usually referred for a closer look and sometimes a small biopsy.
Benefits and limitations
Possible benefits
- Finding cancer earlier, when treatment may be simpler
- Preventing some cancers by treating pre-cancer
- Lower risk of dying from the screened cancer, for proven programmes
- Reassurance for many people
Possible harms
- False alarms, extra tests and worry
- Missed cancers and false reassurance
- Overdiagnosis and treatment that was not needed
- Discomfort, time and sometimes cost
False positives and false negatives
No test is perfect.
- A suggests a problem when there isn't one. It leads to more tests, which usually turn out normal.
- A misses something that is there. This is why new symptoms matter even after a normal result.
This is why a recall letter is not a diagnosis. Want to explore the maths? The interactive video Can one blood test find cancer early? lets you change a test's accuracy and see what happens to false alarms.
Overdiagnosis, explained gently
Some cancers grow so slowly that they would never cause symptoms or shorten a person's life. Screening can find these too. This is called .
Overdiagnosis is not a doctor's mistake. At the time of diagnosis, it is usually impossible to tell which cancers would stay harmless, so they are treated. For some cancers, such as some prostate cancers, careful monitoring (active surveillance) is now offered instead of immediate treatment.
Knowing about overdiagnosis is part of making an informed choice about screening. It is not a reason to fear screening.
Access barriers
Screening only helps people who can reach it. Common barriers include cost, distance, time off work, caring responsibilities, language, disability access, fear, and past experiences of being treated unfairly.
- Ask whether screening is free or subsidised where you live.
- Ask about evening or weekend appointments, mobile units, or home self-sampling (for example HPV or bowel tests).
- You can request an interpreter, a chaperone, or adjustments for disability.
How to prepare for screening
- Check the invitation or ask what the test involves and how long it takes.
- Note any symptoms: if you have one, raise it separately, as it may need a diagnostic test.
- Bring a list of medicines and any relevant history, such as previous results or surgery.
- Ask how and when you will get the result.
- Bring someone with you if it helps.
What an abnormal screening result may mean
An abnormal or "positive" screening result means something needs a closer look. It does not mean you have cancer. Most people with an abnormal screening result do not have cancer.
Next steps depend on the test and may include a repeat test, more detailed imaging, a camera test such as colposcopy or colonoscopy, or a biopsy. Ask:
- What exactly did the result show?
- What are the next steps, and how soon?
- Who will explain the results?
Waiting is hard. See coping while you wait for results.
Screening readiness checklist
Answer a few general questions to see topics you may want to discuss with a clinician. Your answers stay in your browser.
Age range
Sex assigned at birth
Screening depends on the organs you have. Trans and non-binary people can ask a clinician which programmes apply to them.
Family history of cancer
Smoking history
Chewing tobacco, paan or gutka
What best describes you today?
Topics you may want to discuss with a clinician
Updates as you answer. Not a recommendation.
Frequently asked questions
What is the difference between screening and a diagnostic test?
Screening tests people who feel well and have no symptoms, to find cancer or pre-cancer early. Diagnostic tests are used when there is a symptom or an abnormal result, to find out what is causing it. If you have a symptom, you need a diagnostic assessment, not a screening appointment.
I was called back after screening. Does that mean I have cancer?
Usually not. Recalls happen when images or results need a closer look. Most people who are recalled do not have cancer. It is normal to feel anxious while waiting; see our guide to waiting for results on the support page.
What does overdiagnosis mean?
Overdiagnosis is when screening finds a cancer that would never have caused symptoms or harm. At diagnosis it is usually impossible to tell which ones those are, so some people have treatment they did not need. This is one of the trade-offs to understand before screening.