A pack-year is a clinical
quantification of
cigarette smoking
Tobacco smoking is the practice of burning tobacco and ingesting the resulting smoke. The smoke may be inhaled, as is done with cigarettes, or simply released from the mouth, as is generally done with pipes and cigars. The practice is believed ...
used to measure a person's exposure to
tobacco
Tobacco is the common name of several plants in the genus '' Nicotiana'' of the family Solanaceae, and the general term for any product prepared from the cured leaves of these plants. More than 70 species of tobacco are known, but the ...
. This is used to assess their risk of developing
lung cancer
Lung cancer, also known as lung carcinoma (since about 98–99% of all lung cancers are carcinomas), is a malignant lung tumor characterized by uncontrolled cell growth in tissues of the lung. Lung carcinomas derive from transformed, malign ...
or other pathologies related to tobacco use. However, it is difficult to rely on the assessment based on the pack-year due to the different nature of the packaging by different companies.
Definition
The pack-year is a unit for measuring the amount a person has smoked over a long period of time. It is calculated by multiplying the number of packs of
cigarettes smoked per day by the number of years the person has smoked. For example, 1 pack-year is equal to smoking 20 cigarettes (1 pack) per day for 1 year, or 40 cigarettes per day for half a year, and so on.
[http://www.cancer.gov/dictionary?CdrID=306510 National Cancer Institute definition of pack year]
One pack-year is the equivalent of 365.24 packs of cigarettes or 7,305 cigarettes, in a year as smoker.
Calculation
Number of pack-years = (packs smoked per day) × (years as a smoker)
''or''
Number of pack-years = (number of ''cigarettes'' smoked per day/20) × number of years smoked.
(1 pack has 20 cigarettes in some countries)
Note that despite the unit being called a "pack-year," the actual unit is simply a number of packs (as noted above).
:
For example: a person who has smoked 15 cigarettes a day for 40 years has a (15/20) x 40 = 30 pack-year smoking history.
''One'' pack-year is smoking 20 cigarettes a day for one year. If someone has smoked 10 cigarettes a day for 6 years they would have a 3 pack-year history. Someone who has smoked 40 cigarettes (2 packs) daily for 20 years has a 40 pack-year history.
Significance and usage
Quantification of pack-years smoked is important in clinical care, where degree of
tobacco
Tobacco is the common name of several plants in the genus '' Nicotiana'' of the family Solanaceae, and the general term for any product prepared from the cured leaves of these plants. More than 70 species of tobacco are known, but the ...
exposure is correlated to risk of disease such as lung cancer
and heart disease.
References
{{reflist
Smoking
Medical tests