From the Guidelines
Packs per year of cigarette smoking is calculated by multiplying the number of packs of cigarettes smoked per day by the number of years the person has smoked, with 1 pack-year defined as smoking 20 cigarettes/day for 1 year. This calculation is based on the definition provided by the National Cancer Institute (NCI) Thesaurus, as referenced in the 2020 American College of Cardiology/American Heart Association task force report 1. To determine pack-years, one must first calculate the number of packs smoked per day, taking into account that 1 pack contains 20 cigarettes. For instance, if an individual smokes 10 cigarettes daily, this equates to 0.5 packs per day.
Calculation Example
- If someone smokes 10 cigarettes per day for 15 years, the calculation would be: 0.5 packs/day × 15 years = 7.5 pack-years.
- For someone smoking 2 packs daily for 20 years, the calculation is: 2 packs/day × 20 years = 40 pack-years. This calculation is crucial in clinical practice as it quantifies cumulative smoking exposure, which directly correlates with the risk for smoking-related diseases such as chronic obstructive pulmonary disease (COPD), lung cancer, and cardiovascular disease, as noted in various studies including those referenced by the Institute of Medicine Committee on Secondhand Smoke Exposure and Acute Coronary Events 1.
Clinical Importance
The pack-year calculation is used by healthcare providers to:
- Assess disease risk
- Determine screening needs, such as lung cancer screening for those with ≥30 pack-years
- Evaluate the potential benefit of smoking cessation interventions The relationship between pack-years and disease risk is dose-dependent, meaning higher pack-years correlate with progressively higher health risks, emphasizing the importance of accurate calculation and consideration of smoking history in patient care 1.
From the Research
Calculation for Packs per Year of Cigarette Smoking
The calculation for packs per year of cigarette smoking can be determined by the following formula:
- Number of packs smoked per day multiplied by the number of years smoked Some studies provide evidence for this calculation, including:
- A study published in the Journal of the National Cancer Institute 2 which mentions that a 68-year-old man who has smoked two packs per day for 50 years
- A study published in Pulmonary pharmacology & therapeutics 3 which mentions that smoking pack-years 37 ± 3.5 vs. 22 ± 12
- A study published in Tobacco control 4 which developed a formula for converting loose tobacco use to pack years smoked, based on the weight of tobacco in ready made cigarettes
Factors Influencing Packs per Year
Several factors can influence the calculation of packs per year, including:
- Type of tobacco used (e.g. loose tobacco or ready-made cigarettes) 4
- Number of cigarettes smoked per day 2
- Duration of smoking in years 3, 2
- Weight of tobacco in ready made cigarettes 4
Relationship between Pack Year and Lung Function
Research suggests that there is an inverse relationship between pack year and lung function parameters, including: