Asthma is difficult to define; physicians may use ICD-9 codes for nonspecified bronchitis, chronic bronchitis, emphysema or chronic airflow obstruction instead of asthma when seeing a patient . Further, 20% to 50% of those reporting asthma attacks or medication use who had not visited a physician for asthma in the five years before the survey (false-negative) did see a physician for another, potentially overlapping respiratory diagnosis (bronchitis, chronic airflow obstruction). Still, approximately 20% of subjects reporting asthma attacks or medication use did not visit a physician for any respiratory diagnosis within the five years before the survey.
In the absence of a generally accepted definition of asthma , physicians appear to have problems diagnosing the disease and explaining it to their patients. Patients with similar symptoms can be labelled as asthmatic or can be given another respiratory diagnosis. Some patients labelled as asthmatic at a physician contact were apparently not aware of it.
Not all patients with symptoms go to see a physician, particularly if their asthma is not severe. Although the vast majority of people with asthma attacks or medication use in the previous year reported confirmation of their asthma by a physician during their lifetime, many had not seen a physician for a respiratory problem in the previous five years. Some contacts with physicians for asthma were probably lost, because only one diagnosis could be listed as the reason for a physician visit. Patients may have seen their physicians for other health problems; their asthma could have been diagnosed and even treated with medication without appearing on the claim for payment. We do not know how often this happened, but in the age group studied, comorbidities were likely relatively few.