Below is a list of answers to the most frequently asked questions about the smoking pack years calculator. This version was prepared by Dr Nigel Masters and Catherine Tutt RN, RM and updated on 1st October 2023.
- Why record the patient’s smoking history numerically on the computer medical record?
- What numbers should be recorded to describe smoking exposure?
- Why have a computerised clinical smoking load/pack years calculator?
- Is there any evidence that smoking load is useful in clinical settings?
- Why do you use cigarette pack years as clinicians find it difficult to work with?
- Will computerised clinical systems need to undergo changes to incorporate the smoking calculator?
- Will the clinical smoking calculator be used in primary care research?
- How have you arrived at the clinical smoking load calculator mathematics?
- Does the smoking load calculator record passive smoking?
- Who are Masters and Tutt?
- Why Does the Pack Year Calculator not Record Vaping?
1.Why record the patient’s smoking history numerically on the computer medical record?
Numbers linked to patients can be searched easily to identify at risk groups. Examples include blood pressure readings, body mass index and Haemoglobin A1c.
2.What numbers should be recorded to describe smoking exposure?
One important measure for smoking exposure in patient’s histories is smoking duration in years. Smoking duration is known to have strong links to smoking related diseases and is considered the best way to record patient smoking exposure by epidemiologists. At present this cannot be coded in 2016 NHS medical computer records as smoking is documented by SNOMED CT code descriptors e.g. ex-moderate smoker (10-19/ day). Smoking duration can be noted as free text but is not searchable or widely used by practicing medical staff.
Starting dates and stopping dates of smoking are important to ascertain time of exposure in a patient‘s timeline as some smoking related diseases appear to be age dependent and decline on stopping smoking .
A common single number used by clinicians is smoking pack years (one pack year is equivalent to 20 cigarettes smoked daily for one year) which can be recorded on most medical computer systems. This has been difficult to record as many smokers vary their smoking habits but the pack year calculator makes this easy. Nevertheless pack year numbers have limitations in that 5 cigarettes a day smoked for 20 years is the same as 20 cigarettes smoked for 5 years i.e. 5 pack years for both but the risk of smoking related ill health is very much greater in the former smoker. Thus although we advocate the use of numbers to record smoking history it is only a crude imprecise description of smoking related exposure .
In conclusion starting and stopping dates, smoking duration in years and smoking pack years should be recorded for each patient so that smoking exposure risks can be taken into account when patients present with symptoms of disease. This numerical smoking recording would also be helpful in smoking related disease screening, epidemiological studies and planning health care interventions.
3.Why have a computerised clinical smoking load/pack years calculator?
Smoking is a leading cause of preventable morbidity and premature mortality in developed and developing countries.
As such, clinicians need to work out total cigarette load at the consultation to attempt individualised disease prediction. To be effective this information needs to be highly visible on the patient’s summary screen.
At present computerised systems only record basic smoking data, i.e. ex-smoker, 20 cigarettes a day, non-smoker etc.
With the introduction of computers there are many calculators available to the clinician such as the Framingham Cardiovascular Score and eGFR kidney disease measure, but it could be argued that the smoking pack year calculator is more helpful and predictive of disease. For example eye maculopathy is strongly associated with a 40 pack year history.
Some smoking histories can be complicated and a calculator simplifies the task and provides a universal standard for smoking load/pack year recording, across all Healthcare settings.
4. Is there any evidence that smoking load is useful in clinical settings?
One practice is effectively using smoking load to screen its population of active or ex smokers.
By using case finding and carefully recording smoking load, patients were selected for spirometry screening as an aid to detecting chronic obstructive pulmonary disease (COPD).
Ex-smokers or active smokers with a smoking load greater than 15 pack years were invited for spirometry screening entitled ‘a free lung check’! Up to 56% of those offered this free check attended screening.
Please note that this referral process simply involved using smoking load rather than symptoms as the key to screening.
Often patients with COPD do not have symptoms and/or are in denial of their symptoms. The spirometry screen in this group of patients had a 28% diagnosis rate.
As a result of this approach the practice increased the number of patients on its COPD register.
In addition targeted smoking advice could be given to this needy selection of patients if they wished.
(Nigel Masters, Catherine Tutt, Jenny Eades. Early diagnosis of COPD. British Journal of General Practice December 2006 page 969.)
Smoking load should be recorded on clinical summaries so that information can be transferred between clinicians and healthcare systems. For example radiologists having smoking load recording on chest X-ray forms will be more sensitised to look for smoking related disease. This will benefit smokers and clinicians alike!
5. Why do you use cigarette pack years as clinicians find it difficult to work with?
Pack years is a vital smoking load tool used by epidemiologists but can be difficult to use in a non-computerised environment as the calculation can be difficult. Changing smoking patterns over an individual’s lifetime and the use of loose tobacco can complicate what seems a simple calculation. One pack year is equivalent to 7300 cigarettes smoked (i.e. 20 cigarettes smoked per day for 1 year divided by 20).
6. Will computerised clinical systems need to undergo changes to incorporate the smoking calculator?
At present because of inadequate SNOMED CT codes it is difficult to record simply whether a patient is a current smoker of X amount of pack years or an ex-smoker with X amount of pack years, so it is necessary to free text the number of pack years on the summary. A small change in the systems will lead to easy dissemination of this vital piece of clinical information.
7. Will the clinical smoking calculator be used in primary care research?
The smoking load information on individual patient records should be useful in research. Certainly the General Practice database should incorporate this feature in future and it could explore the value of this item for research developments.
8. How have you arrived at the clinical smoking load calculator mathematics?
The smoking load calculator has used readily derived conversion figures which have been taught at Education for health www.educationforhealth.org (formerly National Respiratory Training Centre) at Warwick, England over the last 12 years. These figures have also been supported by a recent brief report which was done by Wood DM et al, called “Pack year” smoking histories: what about patients who use loose tobacco? Tobacco Control 2005; 14:141-142.
This is not an exact science and approximations have been made, e.g. a cigar is considered equivalent to 4 cigarettes and a cigarillo is considered equivalent to 2 cigarettes. Cigarillos are a small, thin type of cigar such as a Hamlet or Cafe Creme. One pack year is equivalent to 7300 cigarettes smoked (i.e. 20 cigarettes smoked per day for 1 year divided by 20). Loose tobacco estimates that 25 grams (1oz) has been approximated to the equivalent of 50 cigarettes. One Pipe is equivalent to two and a half cigarettes.
The calculation also relies on the patient giving an accurate history which can be determined by asking patients to recall what they smoked in each decade of their life.
Despite these limitations it provides a simple way to record this important disease risk factor. Those individuals who continue to smoke should have their pack years recalculated every five years.
9. Does the smoking load calculator record passive smoking?
It does not record passive smoking. One description that may be useful is the definition of a passive smoker as someone who has lived in the same house as a smoker for five years.
10. Who are Masters and Tutt?
Nigel Masters is a retired general medical practitioner who is a keen innovator of simple ideas for the efficient delivery of primary care for patients. He introduced the first polypropylene footpump nebuliser for drug delivery . He has won awards for his development of clinical indications on prescription . Visit the website www.clinicalindications.co.uk. He has developed simple paediatric dosing calculators such as the Dexamethasone liquid treatment dose calculator for croup . This calculator is free to those who request it on the enquiry page.
Catherine is a retired Practice Nurse Specialist with a special interest in Respiratory Care who has widely lectured on both asthma and COPD.
Nigel Masters and Catherine Tutt won the 2006 National Guidelines in Practice Award COPD section for their holistic approach to COPD care.
As a result of their combined decision to be more proactive in the detection of often asymptomatic COPD patients, they recognised the need for a simple pack year calculator. The first working version was produced in Excel by Caroline MacFarlane in January 2007 and tested at Highfield surgery in a clinical setting for three months in early 2007. Jenny Eades Medical Student at Imperial College undertook the first critical and detailed audit of smoking load recording in the detection of early COPD.
At lectures on their innovative approach to COPD management in primary care Nigel and Catherine were asked to provide the calculator to other healthcare teams and with the help of James Gardner produced a web-based version free to all users. Jessica Masters Research Assistant has worked on audits in the practice showing sustained improvements in pack year recording and increasing levels of COPD detection throughout early 2007 when the calculator became available.
11. Why Does the Pack Year Calculator not Record Vaping?
The pack year calculator records combustible smoking products only. Years vaped may be the best way to record vaping on the clinical record.