Epidemiology of advanced lung disease in the United States

Advanced lung disease (ALD) may be defined as a chronic, nonmalignant lung disease that permanently impairs activities of daily living. Defined in that fashion, the term encompasses the severe end of the spectrum of many common and unusual lung diseases, including asthma, chronic obstructive pulmonary disease (COPD), cystic fibrosis (CF), sarcoidosis, the pneumoconioses, idiopathic pulmonary fibrosis, and pulmonary hypertension. Like ''end-stage kidney disease,'' the term advanced lung disease is useful clinically because supportive treatment is similar regardless of the original cause of organ injury. Many, but not all, patients with ALD are disabled. ALD is identified by a physician on the basis of history, physical examination, and appropriate diagnostic studies, and is related to functional impairment. Disability is determined by an insurance administrator or administrative law judge and, in adults, is related to ability to work.(42) Mortality statistics maintained by the National Center for Health Statistics (NCHS) indicate that COPD and allied conditions are the fifth leading cause of death in the United States, after heart disease, cancer, accidents, and neurologic disease(12) (Fig. 1). There was a 46.6% increase in the death rate for chronic lung disease from 1979 to 1993, and a 7.5% increase from 1992 to 1993.(12) The mortality statistics probably underestimate the mortality attributable to ALD because many individuals who are severely impaired by smoking related chronic lung diseases actually die of other causes, notably heart disease or cancer.(44) This review focuses on US data, although the burden of ALD worldwide obviously is more substantial. The NCHS is the principal source of information on morbidity and mortality in the United States. It-obtains information through several population-based surveys of representative samples of specific data sources(45) (Table 1). Each of the surveys conducted by the NCHS provides data that are used to estimate some measure of disease incidence or prevalence, health care utilization rate, or death rate. Data are estimated and reported principally for diseases with high incidences, such as asthma and COED. Data on more rare conditions, such as CF, are generally obtained from disease registries (when they exist), or from large health care delivery databases, such as health maintenance organizations. Regardless of the source of information, it is not always possible to determine the distribution of illness severity from databases. As a result, many are less useful for assessing the extent of ALD, as previously defined.