The number of pack years in our life is a measure of how much we have smoked. It is not, contrary to what the term implies, the number of years we have smoked. That's only one aspect of the math involved in calculating pack years. The other factor is how much we smoked per day over that period.

Doctors can utilise pack years to determine someone's risk of lung cancer, because the number of cigarettes smoked is directly related to risk of developing cancer. Doctors can utilise pack years to assess the risk of other diseases as well which are related to smoking such as heart disease, lung condition, peripheral vascular disease and others.

In studies on smoking, researchers also utilise pack years as a conventional approach to measure data.

Pack years calculation

To figure out someone's pack-year history, two pieces of information are needed:

The number of cigarettes smoked on a daily basis (N)

The amount of years you've been a smoker (T)

These figures can be used to calculate pack years (PY) using the formula below:

PY = N x T

Lung Cancer risk

The number of times one has smoked may be a significant factor in determining their potential risks of lung cancer.

Health professionals, on the other hand, are more likely to use the number of pack years to assess cancer risk, taking into account the amount and duration of smoking.

In general, the longer one has been a smoker, the higher their cancer risk. 

Limitations

While the number of pack years a person has smoked can help determine risk, it isn't always accurate.

Female smokers, for example, appear to get lung cancer after fewer pack years than male smokers. According to some research, this is due to women's higher vulnerability to carcinogens in cigarettes, which pack years do not account for.

Pack years may not be the best way to quantify adults with chronic obstructive lung disease (COPD).

The fact that lung cancer can occur in never-smokers is also ignored when risk is linked to pack years.

Current and former smokers

Current smokers are at a higher risk of smoking-related health problems, but they aren't alone. Those who have never smoked or who smoke infrequently have a higher lifetime risk of sickness. Likewise quitting for a small time as well has immense health benefits which means that it’s never too late.

A research on heart-related sickness reveals that the risk of heart disease in smokers may not be proportional to the number of pack years smoked. Rather, current smoking patterns are the most important factor. Former smokers were found to have a significant reduction in their risk of heart attack, stroke and other cardiac disorders after quitting smoking.

Screening for Lung Cancer

Screening is the method recommended for health individuals, who otherwise maybe at risk of cancer. Here we are talking about Lung Cancer risk amongst smokers. A low dose CT scan of chest (Computerised Tomography) done for cases at higher risk as assessed by an oncologist is recommended when smoking history is significant. 

Prevention and aarly diagnosis remains the key here.