The controversy on how to label OLDs has been around for decades,14–
debating whether it is generalized OLD, chronic nonspecific lung disease, COPD, or another term that fits the best. The so-called Dutch hypothesis on the interrelationship of OLD, initially described by Orie15
in 1961, stated that asthma and bronchial hyperreactivity predispose patients to develop COPD later in life, and this theory has not yet been ruled out. Practical implications in this debate are relevant because the management guidelines for asthma and COPD differ. However, a growing number of researchers and clinicians consider that respiratory disease is a continuum from childhood to adulthood, and that asthma leads to chronic OLD becoming COPD in the elderly. Indeed, many physicians treat adult chronic asthma patients and COPD patients with similar drugs. In our study, it was not possible to establish any difference between the GPs and pulmonologists as to how the diagnoses were made. All entries in the GPRD were from GPs only, as the GPRD is a database of primary care doctors only, while NHANES III is a survey of self-reported diagnoses and conditions by the participants. Regrettably, in these two countries and elsewhere, OLD is diagnosed too often without spirometry findings. It may be timely to remind primary care physicians that they should accurately assess the airway status of their patients. It takes only a few minutes to inquire about medical history, to examine patients’ lungs, to confirm their impression with spirometry followed by a course of appropriate therapy, and finally to educate patients on the correct use of inhalers. Overall, only about half of the patients who reported a COPD-compatible diagnosis in the NHANES III survey had abnormal spirometry findings corresponding to grade 1 (or higher) of the GOLD guidelines.4
If the diagnosis was based on spirometry as well as clinical features, the distribution of the various COPD diagnoses would alter considerably (Fig 4)
. Our finding that US NHANES III participants with an emphysema-only diagnosis had a lower prevalence of objective airflow obstruction than did participants with concomitant emphysema and asthma or chronic bronchitis might seem to be counterintuitive. If these results are confirmed in other studies, the current practice in COPD randomized controlled trials (RCTs) of excluding patients who have been diagnosed with concomitant COPD and asthma, or COPD patients who have some asthmatic component (ie, positive results of a bronchodilator test or methacholine challenge, or atopy) might be artificial and would not represent the spectrum of OLD patients represented in the community. Asthma RCTs usually recruit patients who are extremely young, do not smoke, and have mild disease, and whose condition are completely reversible. Conversely, COPD RCTs tend to recruit patients who are old, smoke, and have severe disease, and whose conditions are largely irreversible and include emphysema. Therefore, “mixed” patients are not recruited into RCTs. Physicians often have difficulties in labeling patients as having COPD or asthma among those in the large group of aging, chronic OLD patients with a history of cigarette smoking and an asthmatic component. Indeed, evidence-based medicine cannot be conducted in patients with combined asthma and COPD, who, according to our research, account for as much as half of the OLD population aged ≥ 50 years.