Results

Questionnaires were returned by 4792 (80%) of the 6000 subjects to whom they were sent. Their ages ranged from 65 to 104 years (median 74 years) and 2433 (51%) were men. Seven hundred and eight (14.6%) indicated that they were using bronchodilators, corticosteroids, or sodium cromoglycate for respiratory disease. Of the remaining 4084, 55 reported a doctor's diagnosis of asthma at some time and a further 696 reported symptoms suggestive of asthma. In addition, 1566 had other respiratory symptoms such as cough and phlegm, and 1767 had no respiratory symptoms.

A total of 501 participants were randomly selected for lung function tests, of whom 280 (56%) completed spirometric and/or serial PEF measurements. Table 2 shows the distribution of these men and women according to their symptoms and history of diagnosed asthma. The reasons for failure to complete lung function tests were refusal (n=129), illness (n=34), death in the interval after completing the questionnaire (n=9), change of residence or general practice (n=8), and difficulty with the measurement techniques (n=41). Corticosteroid trials were completed by 21 (12 oral and nine inhaled treatment) of 41 eligible individuals. Of the remainder, seven agreed but withdrew before completion because of minor side effects, six refused, and seven had contraindications.

Table 3 shows the distribution of those tested for asthma by sex, age, and smoking habits. The individuals who were tested for asthma included a higher proportion of men (59%) and were younger (median age 72) than the population from which they were selected (50% men, median age 74).

On testing, 38 individuals were found to have asthma according to the pre-specified diagnostic criteria. Of these, 19 had airflow obstruction that was reversible in response to salbutamol and ipratropium bromide, and 24 showed significant diurnal variation in PEF. The corticosteroid trials did not reveal any additional cases of reversible airflow obstruction. On the basis of lung function testing, the asthma was classified as mild persistent in six individuals, moderate persistent in 14, and severe persistent in 18. Table 4 gives the prevalence and severity of untreated asthma in each of the symptom groups sampled. The largest number of cases (n=20) was found in symptom group 1 (wheeze or daytime breathlessness at rest at least once per month), and this represented 13% of those tested in this group. The highest prevalence (21%) was found among those reporting a previous diagnosis of asthma by a doctor, but who were not currently on treatment, followed by those in symptom groups 1, 2, and 5 (13–20%). None of the individuals in symptom group 3 (nocturnal breathlessness in the absence of wheeze or daytime breathlessness) had evidence of asthma on lung function testing.

To explore the dependence of our findings on the diagnostic criteria we adopted, the number of subjects with untreated asthma was estimated using several alternative definitions for the disorder. With the daily variability in peak flow redefined as (PEFmax—PEFmin)/0.5(PEFmax + PEFmin), the number of cases was 42. If, in addition, reversibility of airflow obstruction with bronchodilators was redefined as an increase in FEV₁ amounting to at least 9% of the subject's predicted FEV₁, the number of cases was 41.10A larger difference was found if the criteria for accepting PEF readings were extended to include triplets in which the highest value was up to 40 l/min more than the second highest reading. With the original definitions of variability and reversibility, the number of cases then increased to 63.

Table 5 shows the estimated prevalence of untreated asthma in the study population by sex, age, social class (based on the last occupation or that of the husband), and smoking habits. For comparison, the estimated prevalence of treatment with respiratory medication (bronchodilators, corticosteroids, or sodium cromoglycate) is also given for the same population groups. Overall, the estimated prevalence of untreated asthma was 1.7% (95% CI 1.2% to 2.3%). It was higher in men (2.4%, 95% CI 1.6% to 3.6%) than in women (1.2%, 95% CI 0.7% to 2.1%), the difference being most marked at older ages. In contrast, estimated rates of treatment with respiratory medication were similar in the two sexes. Untreated asthma was most common in current smokers.

Discussion

This study found untreated asthma in an estimated 1.7% of adults aged 65 years or older, and in most cases (84%), according to levels of impaired lung function, the disease was moderate or severe. Participants who reported episodes of wheeze or breathlessness at rest or a history of past asthma were most likely to show objective evidence of active disease. The use of alternative criteria for defining reversibility had little influence on the prevalence rate of untreated asthma. In contrast, resetting our limit for acceptable blow to blow variability of PEF readings from 20 l/min to 40 l/min almost doubled the number of subjects identified as having untreated disease.

The main strengths of this study were the population approach, the high response rate to the initial questionnaire (80%), and the relatively high response rate to lung function testing (56%), taking into account the older age of the participants. We chose only to investigate individuals reporting symptoms characteristic of asthma, thus excluding those who only reported symptoms such as phlegm or were asymptomatic. Our previous work has shown that older people who only report symptoms such as phlegm or have no respiratory symptoms are unlikely to have objective evidence of airflow limitation or bronchial hyperresponsiveness.11

There were limitations to our protocol for lung function testing which may have led to some misclassification of participants. Airflow obstruction was defined using the FEV₁/FVC ratio with a cut off of 70% or lower. As the FEV₁/FVC ratio declines with increasing age, this approach may identify a proportion of healthy elderly subjects without airways disease.12 Although this might have increased the apparent frequency of airflow obstruction within our sample, it would not have contributed to the prevalence of untreated asthma as reversibility and significant PEF variability are unlikely to be found in healthy elderly people without airways disease. Also we only carried out bronchodilator reversibility testing on one occasion and did not use high dose bronchodilators. Performing reversibility testing on more than one occasion and use of higher dose bronchodilators can increase the number of subjects found to have reversible airflow obstruction.13 ,14 Gannon and colleagues have shown that significant PEF variability will be found more frequently in subjects in whom PEF is measured at least four times daily compared with twice daily as in this study.15 This may have resulted in a degree of underestimation of the prevalence of untreated asthma within our sample.

Most other studies in this age group have concentrated on undiagnosed asthma whereas we chose to look at untreated disease. It is unclear why some patients with diagnosed asthma and ongoing disease were not on treatment. Some may have had asthma that remitted and then recurred. Others may have stopped treatment.

Our results agree with those of a recently performed study in Lincolnshire, UK in which undiagnosed asthma was found in 2.2% of a single practice random sample of 353 patients aged 60–75 years.16 This study had a similar protocol for lung function testing. Individuals who were identified as having newly diagnosed asthma in that study were not considered to have severe disease as measured by pulmonary function and health status assessment. In contrast, in our larger community sample of untreated asthmatics, using a different approach to assess asthma severity, 84% of our cases had moderate or severe disease. As with other studies that have examined the prevalence of untreated asthma in older people, we found that investigation of many untreated individuals with symptoms suggestive of asthma failed to show airflow limitation on lung function testing.16 ,17 The causes of their symptoms are unclear but a proportion may have had cardiac disease or transient symptoms related to infections.

The costs of screening for untreated asthma were not evaluated in our study, but a Dutch investigation has estimated that the identification of new cases of asthma or chronic obstructive pulmonary disease in an adult population subjected to a screening programme cost $500–1000 per case.18 We found that the prevalence of untreated asthma was higher in men than in women, particularly in the older age group (75+). There is some evidence that, in men and women with similar symptoms suggestive of asthma, men are less likely to receive a label of asthma and more likely to be considered as having smoking related airways disease.19 ,20

Our results should help general practitioners to identify patients who are most likely to benefit from lung function testing. They suggest that, in older adults with a past diagnosis of asthma and/or current wheeze or breathlessness at rest, about 15–20% may have asthma. Uncontrolled asthma is considered to account for a significant proportion of health care spending on the frequent exacerbations requiring emergency primary or secondary care.21Appropriate treatment and monitoring of asthma should result in health gains. Our results do not suggest that large scale screening for untreated asthma in elderly people is likely to be cost effective. Case finding among those at high risk and therapeutic trials of treatment would seem to be a more efficient approach deserving formal evaluation.

Future research should focus on defining the pattern of risk factors that best predicts untreated asthma, and on understanding the patient, practitioner, health and social factors that may contribute to the phenomenon.