American Journal of Respiratory and Critical Care Medicine

We analyzed mortality trends among people who died with a diagnosis of obstructive lung disease from 1979 through 1993, using death certificate reports of 31,314,160 decedents in the Multiple-Cause Mortality Files compiled by the National Center for Health Statistics. Of all the decedents, 2,554,959 (8.2%) had a diagnosis of obstructive lung disease (ICD-9 490 to 493.9, 496) listed on their death certificates; of these 2,554,959 decedents, only 1,106,614 (43.3%) had obstructive lung disease listed as the underlying cause of death. The age-adjusted mortality rate increased 47.3%, from 52.6 per 100,000 in 1979 to 77.5 per 100,000 in 1993. The age-adjusted mortality rate increased 17.1% among men, from 96.3% per 100,000 in 1979 to 112.8 per 100,000 in 1993, whereas this rate increased 126.1% among women, from 24.5 per 100,000 in 1979 to 55.4 per 100,000 in 1993. Over the study period, white males had the highest mortality rates (98.8 to 115.5 per 100,000), followed by black males (77.5 to 100.2 per 100,000), males of other races (38.1 to 58.6 per 100,000), white females (25.5 to 57.7 per 100,000), black females (14.9 to 38.5 per 100,000), and females of other races (10.9 to 20.9 per 100,000). We conclude that mortality related to obstructive lung disease is underestimated in studies that look at only the underlying cause of death. Mortality rates of obstructive lung disease are starting to stabilize among men, but continue to increase among women, reflecting historical smoking trends in these populations.

Obstructive lung diseases (OLD), including chronic obstructive pulmonary disease (COPD), emphysema, and asthma, are leading causes of mortality among both men and women in the United States (1), and OLD-related mortality rates have been increasing both in the United States and in other countries (2-4). Factors associated with OLD prevalence and mortality include tobacco use, atopy, occupational exposures, genetic factors, and air pollution (5-7).

We used the Multiple-Cause Mortality Files (MCMF), a national mortality data base maintained by the National Center for Health Statistics (NCHS), to analyze national mortality trends of OLD for 1979 through 1993. With this data base, we searched for death certificates on which OLD was listed as being present but was not necessarily classified as being the underlying cause of death. This is important because, people who die because of a chronic disease frequently have other diseases present (8). In addition, we searched for comorbid diseases or risk factors that were listed as being present in association with an OLD.

Using the vital records from the individual states, the NCHS annually compiles data from all death certificates filed in the United States. These data contain the International Classification of Diseases (ICD) codes for the underlying cause of death and up to 20 conditions listed on the death certificate. The data also include demographic and geographic information on the decedent. The International Classification of Diseases, Ninth Revision (ICD-9) was implemented in 1979 and was in effect throughout the 15-yr period used in this study (9). The decedents' conditions are recorded in two places on the MCMF: on the entity axis, which contains the conditions exactly as reported on the death certificate, and on the record axis, which is edited by a computerized algorithm known as the translation of axes. This algorithm determines the single underlying cause of death (UCD) from the conditions and their positions as listed on the death certificates, and edits the other causes of death to avoid duplication. Quality assurance of the data is maintained by trained nosologists who code conditions at the state level and, in turn, by nosologists at NCHS who periodically review data from a 10% sample of the submitted death certificates. The result of this process is the MCMF.

We searched the record axis portion of the 1979–1993 MCMFs for records containing ICD codes for OLDs (490 to 493.9 and 496). We searched for individual OLDs, including bronchitis (either unspecified or chronic, ICD-9 490 to 491.9), emphysema (ICD-9 492 to 492.9), asthma (ICD-9 493 to 493.9), and COPD, not elsewhere classified (ICD-9 496). Within the resulting group of death records, we searched for the UCD. In addition, we searched both the entire database and the OLD database for the following conditions associated with OLDs, including lung cancer (ICD-9 162 to 162.9), pneumoconiosis (ICD-9 500 to 506), and tobacco-use disorder (ICD-9 305.1).

We analyzed the rates of deaths associated with OLDs according to decedents' age, race, and gender. Throughout this paper, the rates we report are for any mention of OLD, unless we specifically state we are reporting the rate for OLD as the UCD. We used 1980 and 1990 U.S. census data to calculate rates for 1980 and 1990, the intercensal estimates to calculate rates for 1992, and linear interpolation to estimate population in other intercensal years. We used Chi-square tests of trends (Epi-info; CDC, Atlanta, GA) for significance testing.

Of the 31,314,160 people who died in the United States from 1979 through 1993, 2,554,959 (8.2%) had OLDs listed on their death records. Table 1 shows the age distribution of decedents with OLD and the proportion of the death records for each age stratum that listed OLD. Although OLD was listed on only 8.2% of all the death certificates, it was listed on 11.8% of death certificates for decedents age 65 through 74, and 10.6% of death certificates for decedents age 75 through 84.

Table 1. AGE STRATIFICATION OF ALL DECEDENTS AND DECEDENTS WITH ANY OBSTRUCTIVE LUNG DISEASE  (OLD, ICD-9 490 TO 493.9, 496), WITH ANY OLD AS THE UNDERLYING CAUSE OF DEATH (UCD),  AND WITH ASTHMA (ICD-9 490 TO 493.9) DURING 1979–1993*

Age (yr)All Decedents nNumber of Decedents with OLDOLD as the UCDDeaths with Asthma Present
n% of All Deathsn% of OLD Deathsn% of OLD Deaths
< 1596,278935 0.247550.817418.6
 1–14250,3373,044 1.22,03066.72,13670.2
15–24596,7093,659 0.62,58170.52,82577.2
25–34821,2945,614 0.73,63964.83,89269.3
35–441,082,20315,624 1.47,62948.86,27640.2
45–541,837,78573,842 4.032,91144.610,93614.8
55–644,085,016340,410 8.3149,29643.922,128 6.5
65–747,144,476841,73011.8369,78343.935,740 4.2
75–848,526,525899,61510.6388,72943.234,752 3.9
> 846,364,158370,143 5.8149,09840.317,556 4.7
None listed9,379343 3.714341.718 5.2
Total31,314,1602,554,959 8.21,106,31443.3136,433 5.3

*From the Multiple-Cause Mortality Files, National Center for Health Statistics.

Of the 2,554,959 death records on which OLDs were listed, 1,106,314 (43.3%) specified OLDs as the UCD (Table 1). This proportion was highest among decedents age 15 through 24 and decreased to its lowest level among decedents age 85 and older (Table 1, Figure 1). Over the study period, the proportion of OLDs listed as the UCD among all decedents with OLD listed increased from 41.9% in 1979 to 44.4% in 1993 (p < 0.001, Chi square test of trend). Other UCDs listed on more than 5% of OLD decedents included lung cancer in 210,437 (8.2%) deaths and atherosclerotic cardiovascular disease in 660,533 (25.9%) deaths.

Of the records on which OLDs were listed, 2,453 (0.1%) listed unspecified bronchitis, 96,669 (3.8%) listed chronic bronchitis, 489,247 (19.2%) listed emphysema, and 1,844, 381 (72.2%) listed COPD. Only 237 decedents had codes for two or more of the above OLDs (excluding asthma) on their death records.

Asthma was listed on death records of 136,433 (5.3%) of the decedents who had any OLD listed. Of these 136,433 decedents, 13,987 (10.3%) also had a code for another OLD listed. Although the highest proportion of asthma-related deaths among decedents with OLDs listed occurred among decedents age 15 through 24, almost 90% of asthma-related deaths occurred in people age 45 and older (Table 1).

Lung cancer was listed on 253,479 (9.9%) of the death certificates that listed OLD. Over the study period, 2,098,868 decedents had a diagnosis of lung cancer listed on their death certificates. Thus, OLD was listed on 12.1% of death certificates listing lung cancer. Pneumoconiosis was listed on 19,291 (0.8%) of the death certificates that listed OLD. Over the study period, 56,242 decedents had a diagnosis of pneumoconiosis. Thus OLD was listed on 34.3% of death certificates listing pneumonoconiosis. Tobacco use disorder (ICD-9 305.1) was listed on 72,260 (2.8%) of the death certificates that listed OLD. This proportion increased from 0.5% in 1979 to 5.1% in 1993 (p < 0.001, Chi square test of trend).

The total number of death records listing one or more OLDs increased by 92.0%, from 116,650 in 1979 to 223,929 in 1993 (Table 2). The age-adjusted mortality rate for any mention of OLD increased 47.3%, from 52.6 per 100,000 in 1979 to 77.5 per 100,000 in 1993, and the age-adjusted mortality rate for OLD as the UCD increased 56.8%, from 22.0 per 100,000 in 1979 to 34.5 per 100,000 in 1993. The total number of men who died with OLD present increased 51.8%, from 84,412 in 1979 to 128,105 in 1993, whereas the total number of women who died with OLD present increased 197.2%, from 32,238 in 1979 to 95,824 in 1993 (Table 2). The age-adjusted mortality rate for any mention of OLD increased 17.1% among men, from 96.3 per 100,000 in 1979 to 112.8 per 100,000 in 1993, and the age adjusted mortality rate for OLDs as the UCD among men increased 20.0%, from 39.4 per 100,000 in 1979 to 47.4 per 100,000 in 1993. Both of these rates, however, have remained stable since 1984. Conversely, the age-adjusted mortality rate for any mention of OLD increased 126.1% among women, from 24.5 per 100,000 in 1979 to 55.4 per 100,000 in 1993, and the age-adjusted mortality rate for OLDs as the UCD among women increased 147.2% from 10.8 per 100,000 in 1979 to 26.7 per 100,000 in 1993.

Table 2. TOTAL COUNTS OF DEATHS WITH OBSTRUCTIVE LUNG DISEASE (OLD, ICD-9 490 TO 493.9, 496) AND COUNTS AMONG MEN AND AMONG WOMEN, AND DEATH RATES PER 100,000 POPULATION, AGE-ADJUSTED TO THE 1980 POPULATION, BY YEAR DURING 1979–1993*

YearTotal Decedents with OLDAge-adjusted OLD-related Mortality RatesMale Decedents with OLDAge-adjusted OLD-related Mortality Rates Among MalesFemale Decedents with OLDAge-adjusted OLD-related Mortality Rates Among Females
1979116,65052.684,412 96.332,23824.5
1980128,36556.891,297102.237,06827.6
1981133,91858.193,507102.740,41129.6
1982138,85159.195,579103.043,27231.1
1983150,77663.0101,850107.848,92634.4
1984157,11364.4104,246108.452,86736.5
1985168,24167.7109,925112.458,31639.5
1986172,30868.2110,716111.261,59241.0
1987176,87068.7111,457110.065,41342.7
1988185,66470.8115,419112.170,24544.9
1989193,13172.4117,062111.876,06947.8
1990197,64472.8119,014112.078,54048.3
1991204,08173.6120,366110.583,71550.5
1992207,07573.1120,648108.486,42750.9
1993223,92977.5128,105112.895,82455.4
Total2,554,616 66.61,623,693108.1930,92340.3

*From the Multiple-Cause Mortality Files, National Center for Health Statistics.

343 decendents with no age listed are excluded from this table.

Over the study period, white males had the highest mortality rates (98.8 to 115.5 per 100,000), followed by black males (77.5 to 100.2 per 100,000), males of other races (38.1 to 58.5 per 100,000), white females (25.5 to 57.7 per 100,000), black females (14.9 to 38.5 per 100,000), and females of other races (10.9 to 20.9 per 100,000, Figure 2). Among both white men and white women, the age-specific mortality rates of OLDs increased in older age strata (Figures 3 and 4). Similar patterns were seen among blacks and people of other races (data not shown).

Obstructive lung diseases are a leading cause of morbidity and mortality in the United States. Previous analyses of OLD mortality have used only the underlying cause of death data (2, 10). Over the study period we determined that the rate of OLD-related mortality increased much more (47.3%) than the increase in the proportion of these deaths listing OLD as the UCD (6.0%), indicating the mortality increase is real. However, we could not determine how important a role OLDs played in the death of people who did not have any of these diseases listed as the UCD, with possibilities ranging from an incidental role to a major factor in the death. Over the study period, though, OLDs were listed as the UCD in only 43.3% of the death certificates that listed any OLD. National estimates of the effects of smoking, such as the smoking-attributable mortality, morbidity, and economic costs (SAMMEC) are based solely on UCD data (11). By depending exclusively on UCD data, however, these estimates may fail to account for many decedents in whom obstructive lung disease was an important factor in the death even though it was not the UCD. Although some of these missed deaths may have had a UCD that SAMMEC would classify as tobacco-related (lung cancer or cardiac disease), programs that rely entirely on UCD data may still underestimate the true effects of smoking on the population.

Researchers from Arizona examined death certificates for 577 decedents who were part of a 20-yr longitudinal study of 3,206 people (12). Of 43 decedents with antemortem evidence of severe airway obstruction (FEV1 less than 50% of predicted and a clinical diagnosis of obstructive lung disease), only 10 (23%) had OLD listed as the underlying cause of death, whereas an additional 23 (55%) had OLD listed as a cause of death but not the UCD. Of the 184 decedents with antemortem evidence of mild to moderate OLD (either clinical diagnosis of OLD or FEV1 from 50% to 70% of predicted), five (2%) had OLD listed as the UCD, whereas 35 (18%) had OLD listed as cause of death but not the UCD. Of the 350 decedents with no antemortem diagnosis of OLD, none had OLD listed as the UCD, and only five (1%) had OLD listed as a cause of death but not the UCD. If results of that study are an accurate reflection of what happens nationally, then most decedents with an OLD diagnosis on their death certificate have OLD, although many people with OLD may not have this diagnosis listed on the death certificate.

Our analyses have shown that OLD related mortality rates vary by gender, race, and age. Although we presented only data for any mention of OLDs, the relative rates of the different demographic groups were similar to those we obtained when we evaluated OLDs as the UCD. Overall OLD-related mortality rates among males have plateaued since the mid-1980s, although they are still increasing among men older than 85, whereas these rates among females continue to increase dramatically. These different patterns are probably related both to historical trends of current and former smoking rates and to historical trends in patterns of occupational exposures among men and women (13, 14). Women may also have a different susceptibility to the effects of continued cigarette smoking or smoking cessation than men (15, 16). When we stratified decedents by race and gender, white males had the highest age-adjusted mortality rates, followed by black males, males of other races, white females, black females and females of other races. The pattern is similar to the ever smoking rates among these various groups (13). We have, in a similar analysis, examined lung cancer mortality rates and found that black males have the highest rates, mirroring their higher rates of current smoking (17). The differences between the relative ranking of various race- and gender-specific OLD mortality rates and various race- and gender-specific lung cancer mortality rates may be related to long-term former smokers being more likely to develop OLD than lung cancer (18). We found that OLD-related mortality rates increased, both among men and among women, with increasing age (Figures 3 and 4). These findings support the observation that OLDs are diseases of aging and increase as the population ages.

Although the majority of decedents with OLD had emphysema or COPD listed, more than 136,000 had a code for asthma listed. Over 90% of these asthma-related deaths occurred in people over the age of 34, although a higher percentage of decedents with OLD who were younger than age 35 had asthma listed as being present. Trends in asthma mortality have been studied both in the United States (10) and around the world (19). Most researchers have restricted their analysis of these deaths to decedents from age 5 through 34, because of uncertainty in diagnoses of people younger than 5 and older than 34 (20). Even among decedents age 5 through 34, though, some misdiagnosis may occur (21). We found that among decedents age 1 through 34 yr, OLDs, asthma in particular, were more likely to be the UCD than among decedents in other age groups (Figure 1). Although this reporting may be accurate, it may also represent an increased tendency for clinicians to attribute a younger person's death to asthma among decedents with asthma in these age groups compared with decedents with asthma in other age groups. Even if this tendency to attribute exists, however, asthma is still under reported as an associated condition on death certificates: we would expect 6 to 7% of decedents in the 15 through 34 age group to have asthma (if every person with a diagnosis of asthma had it listed on their death certificate, even if asthma had nothing to do with the death) (22) yet only 0.7% had this diagnosis listed. Another explanation for asthma being more likely to be listed as the UCD in younger decedents might be the presence of fewer comorbid conditions among children and young adults.

An advantage of using the Multiple-Cause Mortality Files is that we can search for comorbid factors. OLDs are thought to be associated with lung cancer (23), and we found that 9.9% of decedents with OLD also had lung cancer listed. Although only 0.8% of all decedents with OLD had pneumoconiosis, we found that 34.3% of decedents with a diagnosis of pneumoconiosis also had an OLD, confirming that OLD is a common complication of pneumoconiosis (14).

Tobacco use is the most important risk factor for the development of OLD (6). Tobacco use disorder (ICD-9 305.1), however, was listed on only 2.8% of the death records that listed OLD. Although this proportion increased from 0.5% in 1979 to 5.1% in 1993, tobacco-use disorder remains under reported. This underreporting of tobacco use disorder is similar to that reported by researchers in Wisconsin, who found that this code (ICD-9 305.1) was listed on only 93 (8.4%) of 1,110 death certificates in which OLD was the UCD (24). This finding can be contrasted with results from a study from Oregon, where physicians have to answer the question on the death certificate “Did tobacco use contribute to the death?” In that study, physicians responded that in 1,919 (76.2%) of 2,520 OLD deaths, tobacco use definitely or probably contributed to the death (25).

Using death certificate data for epidemiologic studies has certain limitations. Death certificate data are not independently validated, and some degree of misclassification inevitably occurs. Death certificates also have no data on the severity of chronic diseases such as OLDs, and data on risk factors such as occupational exposures, family history, and tobacco use are not universally collected.

OLDs are an important cause of mortality in the United States, yet their importance may be underestimated because they are frequently not listed as the UCD. OLD-related mortality rates have stabilized among males overall, although they continue to increase among males age 85 and older and among females. Sustained public health efforts in further reducing smoking and reducing occupational and environmental exposures, along with appropriate intervention in people with early stages of OLD (26) may help reduce the number of people who die from this group of diseases.

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Correspondence and requests for reprints should be addressed to David M. Mannino, M.D., 4770 Buford Highway, M/S F-39, Atlanta, GA 30341.

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