Lung cancer screening is one of the few cancer screening programmes where the eligibility rules are strict, arithmetic, and worth checking yourself — because a lot of people who qualify are never offered it.
The criteria
US Preventive Services Task Force guidance recommends annual low-dose CT screening for adults who meet all three of the following:
- Aged 50 to 80
- A smoking history of at least 20 pack-years
- Currently smoke, or quit within the past 15 years
All three have to be true. Quitting 20 years ago moves you out of the eligible group under current guidance, as does being 45 with a heavy history.
How to count a pack-year
One pack-year is one pack a day for one year. The arithmetic is packs per day multiplied by years smoked.
A pack a day for 20 years is 20 pack-years. Two packs a day for 10 years is also 20 pack-years. Half a pack a day for 30 years is 15, which does not meet the threshold on its own.
People routinely underestimate this, usually by leaving out the heavier years. It is worth doing the sum properly before concluding you do not qualify.
What the scan is and is not
A low-dose CT uses considerably less radiation than a standard chest CT and takes a few minutes with no injection and no dye.
What it does well is find small lung cancers before they cause symptoms, at a stage where treatment works far better. The trial evidence behind the programme showed a reduction in lung cancer deaths in the screened group.
What it does not do is rule out cancer for the year ahead, or detect every cancer. It is also not a general chest check-up, though it does sometimes find unrelated things — coronary calcium, thyroid nodules, emphysema — which come with their own follow-up.
The annual part is the whole point
Screening works because it is repeated. The benefit comes from catching a change between one year's scan and the next, which a single scan cannot do by definition.
A one-off scan mostly produces findings with no baseline to compare them to. If you are not in a position to come back each year, that is worth saying out loud before starting, because it changes the calculation.
If they find a nodule
Most people screened will have something reported. The large majority of these are not cancer — they are old scars, healed infections, and benign lumps that have been there for decades.
Nodules are graded by size and appearance, and the usual next step for a small one is another scan in a few months to see whether it changes. Something that stays exactly the same over time is reassuring in a way that no single scan can be.
This waiting period is genuinely uncomfortable, and it is fair to ask directly: what size is it, what is the estimated likelihood this is cancer, and what specifically would make you act sooner?
Screening does not replace quitting
It is worth being plain about this. Screening finds cancer earlier; it does not lower your chance of getting it. Stopping smoking does, and continues to do so for years afterwards.
The two work best together, and being enrolled in screening turns out to be a reasonable moment to get real help with quitting rather than a reason to postpone it.
What to ask
Do I meet the criteria — and can we work out my pack-years together? Is the programme available through my insurance? If something is found, who follows it up and how quickly? And can I have help stopping smoking at the same time?