Lung cancer screening: who it is for and how it works

What lung cancer screening is

Lung cancer screening uses a low-dose computed tomography (LDCT) scan. The US National Cancer Institute (NCI) describes this as a procedure that uses a low dose of radiation to make a series of very detailed pictures of the inside of the body, with an x-ray machine that scans in a spiral path - which is why it is also called a spiral or helical CT (NCI: Lung Cancer Screening (PDQ)).

The NHS explains why screening matters: lung cancer causes more deaths than any other cancer in the UK, and there are often no signs or symptoms at an early stage. Screening aims to find it earlier, sometimes before symptoms (NHS: Lung cancer screening).

What the evidence shows

NCI reports that screening with LDCT has been shown to decrease the risk of dying from lung cancer in heavy smokers. In the large National Lung Screening Trial, which studied current and former heavy smokers, yearly LDCT for three years was better than chest x-rays at finding early-stage lung cancer and lowered the risk of dying from it. NCI also states that screening with chest x-rays, sputum tests (checking coughed-up mucus), or both, does not decrease the risk of dying from lung cancer. This is why chest x-rays are not used as a lung cancer screening test.

Who is eligible

Lung screening is targeted at people at higher risk because of smoking. It is not offered to everyone.

• United States: the US Preventive Services Task Force (USPSTF) recommends yearly LDCT screening for adults aged 50 to 80 who have a 20 pack-year smoking history and currently smoke or quit within the past 15 years. Screening should stop once a person has not smoked for 15 years, or develops a health problem that substantially limits life expectancy or the ability or willingness to have lung surgery (USPSTF: Lung Cancer Screening, 2021).
• England: the NHS says people aged 55 to 74 who are current or former smokers, are registered with a GP and live in an area where the service runs may be invited for a lung health check. The NHS says targeted lung screening is being rolled out across England, so it is not yet available everywhere.

What is a pack-year? The USPSTF explains that a pack-year is a way of measuring how much someone has smoked: one pack-year equals smoking an average of 20 cigarettes (one pack) a day for a year. So 20 pack-years could mean one pack a day for 20 years, or two packs a day for 10 years.

The USPSTF also says the decision to be screened should involve a discussion of the potential benefits, limitations and harms - known as shared decision-making. If you are not sure whether you qualify, ask your doctor. In England, the NHS suggests contacting your GP surgery to make sure your record shows that you smoke or used to smoke, so that you can be invited.

What happens

In England, the process starts with a lung health check, which may be in person, by phone or online. A health professional asks about your breathing, lifestyle, and family and medical history, and takes your height and weight. Afterwards, the NHS says one of three things happens: no further action if you are not at higher risk; a referral to your GP if breathing or lung problems are found; or an invitation for a CT scan if you are at higher risk.

The NHS describes the CT scan itself: it may be done in a mobile scanning unit in the community or at a hospital, the appointment lasts about 30 minutes, and the scan takes only a few minutes and does not hurt. Results are sent by letter within 4 weeks of the scan. If anything concerning is seen, you may be referred for further scans or tests.

Possible harms

NCI and the USPSTF both stress that screening has downsides as well as benefits:

• False positives - the scan can show something that turns out not to be cancer. NCI notes this can lead to anxiety and to more tests, including invasive procedures that were not needed. A lung biopsy can cause part of the lung to collapse, which sometimes needs treatment.
• False negatives - a scan can look normal even when cancer is present, so new symptoms still need checking.
• Overdiagnosis - finding cancers that would never have caused harm. NCI says it is not clear how often this happens with lung screening.
• Radiation - NCI explains that radiation from repeated scans may increase cancer risk, and that younger people and people at low risk for lung cancer are more likely to be harmed by this than helped, which is one reason screening is targeted.

Our guide to cancer screening explained covers these ideas in more detail.

Screening does not replace quitting

NCI states that tobacco smoking is the most important risk factor for lung cancer and that the best way to prevent lung cancer is not to smoke. The USPSTF says people who currently smoke should be offered help to stop, and the NHS says current smokers at a lung health check will be offered stop-smoking advice. NCI also says that people who quit smoking, regardless of their age, gain substantially in life expectancy compared with those who keep smoking (NCI: Tobacco). A clear scan is not a reason to keep smoking. See reducing cancer risk for more on tobacco.

Sources

• US Preventive Services Task Force: Lung Cancer Screening (2021)
• National Cancer Institute: Lung Cancer Screening (PDQ) - Patient Version
• NHS: Lung cancer screening
• National Cancer Institute: Tobacco

Published and last reviewed: 21 October 2026.