Table of ContentsView AllTable of ContentsCalculating Pack YearsLung Cancer RiskHeart Disease RiskLimitationsCurrent and Former SmokersLung Cancer Screening
Table of ContentsView All
View All
Table of Contents
Calculating Pack Years
Lung Cancer Risk
Heart Disease Risk
Limitations
Current and Former Smokers
Lung Cancer Screening
Pack years is a measure of how much you have smoked in your life. Despite what you might assume from the name, it is not the number of years you have smoked. That’s just one part of the math used to count pack years. The other part is how much you’ve smoked each day during that time.
Researchers also use pack years as a standard way to measure data in studies on smoking and disease.
This article looks at how to count pack years and what the answers may mean for you.
Verywell / Joshua Seong
Two pieces of information are needed to determine someone’s pack-year history:
Those numbers can be plugged into the following formula to determine pack years (PY):
N x T = PY
This table offers some examples of pack-year calculations.
The length of time you’ve smoked, in and of itself, may be an important factor in determining lung cancer risk.
In general, the more pack years you have smoked, the greater your risk of cancer. If you were looking at a graph plotting data of the two, you’d see them rise together.
In addition to lung cancer, the number of pack years someone has smoked is linked to heart disease as well.
Heart disease accounts for a large percentage of deaths in people who smoke, while secondhand smoke is more likely to lead to heart disease than lung cancer.
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While the number of pack years a person has smoked is a useful tool in determining risk, it is not foolproof.
For example, female smokers appear to develop lung cancer afterfewerpack years than males. Some studies suggest this is because women have an increased susceptibility tocarcinogensin cigarettes—a factor pack years doesn’t take into account.
A 2018 study found that for people withchronic obstructive pulmonary disease(COPD), pack years might not be the best way to measure. How long they’ve smoked was more closely linked with COPD than the “cigarettes per day in pack-years” estimates.
The same study suggests the age someone starts smoking may play an important role as well.
Associating risk with pack years also ignores the fact thatlung cancer occurs in never-smokers. In fact, lung cancer in never-smokers is among the top 10 causes of cancer deaths in the United States.
Current smokers are at high risk for smoking-related health issues, but they’re not the only ones.Former smokersand those who smoke infrequently also have higher lifetime risks of illness.
For example, a study of heart-related illness suggests that the risk in smokers may not be tied to pack years overall. Rather, it is how much they are currently smoking that seems to matter most. Former smokers were found to have a fairly rapid drop in their risk for heart attack, stroke, and related cardiac diseases, once theyquit smoking.
That’s not the case for lung problems, though. One study looked at lung function in more than 25,000 people. Current smokers of just five cigarettes a day or less showed lung function decline that was five times that of former smokers. Even former smokers showed lung damage that lasted for decades.
If you quit smoking, you have a good chance of lowering your risk of cardiac diseases. That is something worth celebrating. The effort to quit isalwaysworthwhile. That said, your risk of lung damage including cancer won’t go away. Unlike heart disease, the risk of lung cancer lasts for decades after you quit smoking and never returns to normal.
One research paper looked at lung cancer in people with 30 pack years or more and found the risk was reduced only gradually for each year they were a former smoker. There was no “dramatic drop-off” after 15 years of quitting.
The same researchers went on to say that lung cancer risk in those withfewerthan 30 pack years is also much higher when compared to never-smokers.
You may be eligible for lung cancer screening and should make sure you are aware of theearly symptoms of lung cancer.
What Percentage of Smokers Get Lung Cancer?
Recap
Pack years of smoking is an important factor in determining who should be screened for lung cancer.
Accordingly, the U.S. Preventive Services Task Force (USPSTF) recommends yearly screening usingcomputerized tomography(CT)for people who:
According to the American Cancer Society, people who are screened with CT are 20% less likely to die from lung cancer than those who havechest X-rays.
The USPSTF also advises that annual screenings should be stopped if:
The American Cancer Society has slightly differing guidelines. They advise not stopping screening 15 years after quitting, but rather continuing as long as a person is healthy and able to get cancer treatment. Otherwise, their recommendations are the same as the USPSTF’s.
What Is CT Lung Cancer Screening?
Summary
Doctors often use pack years to estimate the risk of getting lung cancer. The formula for pack years is based on how much you smoke (cigarettes per day) times the number of years you’ve actively smoked.
Pack years is a useful tool for assessing lung cancer risk, and it gives doctors a standard way to describe that risk in basic terms. Yet it also misses other factors, such as differences between male and female smokers, or how early in life the smoking started.
13 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
National Cancer Institute.Pack year.
American Lung Association.Health effects of secondhand smoke.
Papadopoulos A, Guida F, Leffondré K, et al.Heavy smoking and lung cancer: are women at higher risk? Result of the ICARE study.Br J Cancer. 2014;110(5):1385-91. doi:10.1038/bjc.2013.821
Bhatt SP, Kim Y, Harrington KF, et al.Smoking duration alone provides stronger risk estimates of chronic obstructive pulmonary disease than pack-years.Thorax. 2018;73(5):414-421. doi:10.1136/thoraxjnl-2017-210722
American Cancer Society.Lung cancer risks for non-smokers.
Nance R, Delaney J, McEvoy JW, et al.Smoking intensity (pack/day) is a better measure than pack-years or smoking status for modeling cardiovascular disease outcomes.J Clin Epidemiol. 2017;81:111-119. doi:10.1016/j.jclinepi.2016.09.010
Oelsner EC, Balte PP, Bhatt SP, et al.Lung function decline in former smokers and low-intensity current smokers: a secondary data analysis of the NHLBI Pooled Cohorts Study.Lancet Respir Med. 2020;8(1):34-44. doi:10.1016/S2213-2600(19)30276-0
John Hopkins Medicine.Former smokers: what’s your risk for lung cancer?
US Preventive Services Task Force.Screening for lung cancer: US Preventive Services Task Force recommendation statement.JAMA.2021;325(10):962–970. doi:10.1001/jama.2021.1117
National Cancer Institute.National lung screening trial: questions and answers.
Wolf AMD, Oeffinger KC, Shih TY, et al.Screening for lung cancer: 2023 guideline update from the American Cancer Society.CA Cancer J Clin. 2023;10.3322/caac.21811. doi:10.3322/caac.21811
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