To the Editor:
Supplemental oxygen is a common treatment for individuals with advanced chronic obstructive pulmonary disease (COPD), with a 2010 study estimating that nearly 19% of older adults with COPD use oxygen therapy (1). To date, few population-based studies of supplemental oxygen have been conducted, resulting in several knowledge gaps, including disparities in access to oxygen therapy and the impact of oxygen use on healthcare outcomes (2–5). Medicare is estimated to provide more than 80% of the oxygen prescriptions, suggesting that claims-based data can address some of this research need (6). However, claims-based data are often difficult to access, limited to administrative data, and, for Medicare claims, available only for persons older than 65 years. In contrast, national surveys that use self-reported oxygen can address limitations in claims-based data, as they are publicly available, include participants younger than 65 years, and provide broad information on finances, cognition, physical disability, and social needs. Self-reported supplemental oxygen has not been previously compared with Medicare claims, and this comparison is needed to inform reliability between each approach and interpretation of future studies (7, 8). Our objective was to provide updated prevalence estimates of supplemental oxygen use in a national sample of adults aged 65 years and older and to compare estimates derived from self-reported supplemental oxygen use and linked Medicare claims data.
Methods
Study sample
We used the HRS (Health and Retirement Study), a nationally representative survey of American adults aged 50 years and older, which has collected longitudinal, aging-related data biennially since 1992 (9). We used the 2018 HRS core interview linked with Medicare claims and durable medical equipment claims. We included persons older than 65 years who met criteria for COPD on the basis of self-report and had fee-for-service Medicare claims in the past 2 years (N = 456). This study was approved by the Institutional Review Boards at the University of Michigan and the University of California, San Francisco.
Self-reported and Medicare claims for oxygen use
In those who self-reported COPD, the follow-up question “Are you receiving oxygen for your lung condition?” identified participants with self-reported oxygen use. We identified claims-based oxygen use using any one of Healthcare Common Procedure Coding System codes for key oxygen supplies in the Medicare durable medical equipment (Table 1). We excluded equipment codes for auxiliary supplies such as oxygen tubing, nasal cannula, or humidification systems to maintain high specificity for oxygen supplementation (10).
Table 1.
HCPCS codes used to identify oxygen use in durable medical equipment claims
| HCPCS Code | Description | Number of Claims |
|---|---|---|
| E0424 | Stationary gaseous oxygen system | 0 |
| E0431 | Portable gaseous oxygen | 39 |
| E0434 | Portable liquid oxygen system | 2 |
| E0439 | Stationary liquid oxygen system | 1 |
| E0441 | Stationary oxygen contents, gaseous, 1-mo supply | 0 |
| E0442 | Stationary oxygen contents, liquid, 1-mo supply | 3 |
| E0443 | Portable oxygen contents, gaseous, 1-mo supply | 6 |
| E0444 | Portable oxygen contents, liquid, 1-mo supply | 4 |
| E0465 | Home ventilator, any type, used with invasive interface | 0 |
| E0466 | Home ventilator, any type, used with noninvasive interface | 4 |
| E0470 | Respiratory assist device, bilevel pressure capability, without backup rate feature, used with noninvasive interface | 5 |
| E0471 | Respiratory assist device, bilevel pressure capability, with backup rate feature, used with noninvasive interface | 0 |
| E0472 | Respiratory assist device, bilevel pressure capability, with backup rate feature, used with invasive interface | 0 |
| E1390 | Stationary oxygen concentrator, single delivery port | 87 |
| E1391 | Stationary oxygen concentrator, dual delivery port | 0 |
| E1392 | Portable oxygen concentrator | 21 |
| K0738 | Portable gaseous oxygen, with compressor for home refilling | 10 |
Definition of abbreviation: HCPCS = Healthcare Common Procedure Coding System.Participants may have more than one claim.
Statistical analysis
We determined the national prevalence of supplemental oxygen use with HRS-provided complex survey weights. We calculated the sensitivity, specificity, and Cohen’s kappa for self-reported oxygen use, with Medicare claims codes as the reference. Cohen’s kappa statistic was calculated to describe the concordance between self-report and Medicare claims while accounting for chance agreement. We performed statistical analysis using SAS version 9.4 (SAS Institute) (11).
Results
Of the 456 participants (representing 2.5 million older Americans) who self-reported COPD, 21% (n = 102) self-reported oxygen use, and 18% (n = 88) had Medicare claims for supplemental oxygen (representing approximately 525,000 older Americans). In participants who self-reported oxygen use, the average age was 79 years (standard deviation, 6.9 yr); 60% were women, 19% were Black, 2% were Latinx (Table 2). Among the 88 participants who had Medicare claims, nearly all (n = 78) self-reported supplemental oxygen use (sensitivity, 89%). In contrast, of 102 participants who self-reported oxygen, 78 had Medicare claims for supplemental oxygen (positive predictive value, 76%). Among the 368 people without Medicare claims for supplemental oxygen, 344 did not report oxygen use (specificity, 93%). Of the 354 participants who did not report oxygen use, 344 did not have Medicare claims for supplemental oxygen (negative predictive value, 97%). The kappa coefficient was 0.77, corresponding to moderate concordance between self-reported and Medicare claims for supplemental oxygen (Table 3).
Table 2.
Health and Retirement Study sample characteristics (N = 456)
| Total* | No Self-Reported Oxygen [n (%)]† | Self-Reported Oxygen Use, [n (%)]† | |
|---|---|---|---|
| (N = 456 [100.0%]) | (n = 354 [77.6%]) | (n = 102 [22.4%]) | |
| Age, yr, mean (SD) [range] | 76.8 (7.7) [65–99] | 76.2 (7.8) [65–99] | 79.2 (6.9) [65–97] |
| Female sex | 288 (59.5) | 227 (78.8) | 61 (21.2) |
| Race/ethnicity | |||
| White | 370 (86.9) | 290 (78.4) | 80 (21.6) |
| Black/African American | 59 (7.9) | 40 (67.8) | 19 (32.2) |
| Latinx | 16 (2.7) | 14 (87.5) | 2 (12.5) |
| Other | 11 (2.5) | 10 (90.9) | 1 (9.1) |
| Married | 187 (44.3) | 147 (78.6) | 40 (21.4) |
| Greater than high school education | 332 (77.1) | 261 (78.6) | 71 (21.4) |
| Net worth‡ | |||
| <$6,000 | 94 (20.4) | 65 (69.1) | 29 (30.9) |
| $6,001–$80,000 | 75 (16.5) | 53 (70.7) | 22 (29.3) |
| $80,001–$239,000 | 109 (21.5) | 82 (75.2) | 27 (24.8) |
| ⩾$239,001 | 178 (41.7) | 154 (86.5) | 24 (13.5) |
| Prior or current tobacco use§ | 334 (75.6) | 247 (74.0) | 87 (26.0) |
| Comorbidities‖ | |||
| High blood pressure | 357 (74.5) | 274 (76.8) | 83 (23.2) |
| Heart disease | 265 (57.3) | 197 (74.3) | 68 (25.7) |
| Diabetes | 154 (30.2) | 115 (74.7) | 39 (25.3) |
| Stroke | 79 (16.1) | 53 (67.1) | 26 (32.9) |
| Cancer | 125 (26.6) | 98 (78.4) | 27 (21.6) |
| High depressive symptoms | 146 (34.5) | 107 (73.3) | 39 (26.7) |
| Cognition¶ | |||
| Normal | 301 (70.1) | 251 (83.4) | 50 (16.6) |
| Cognitive impairment, not dementia | 104 (19.3) | 72 (69.2) | 32 (30.8) |
| Dementia | 51 (10.6) | 31 (60.8) | 20 (39.2) |
Definition of abbreviation: SD = standard deviation.
Total percentages in this column are column percentages. Percentages in this column are adjusted for survey weights and thus may not correspond directly to the number listed in each cell.
Percentages for self-reported oxygen and no self-reported oxygen columns are row percentages.
Net worth was calculated as the sum of all assets minus the sum of all debts.
Prior tobacco use was determined by a nested question asked of those who did not report being current smokers: “Have you ever smoked cigarettes?” Current tobacco use was assessed using the question “Do you smoke cigarettes now?”
Comorbidities were self-reported.
Cognition was assessed using Langa-Weir methods.
Table 3.
Contingency tables in self-reported and Medicare claims for supplemental oxygen use and test characteristics for comparison
| Medicare DME Claims for Supplemental Oxygen Use |
||||
|---|---|---|---|---|
| Yes | No | Total | ||
| Self-reported supplemental oxygen use | Yes | 78 | 24 | 102 |
| No | 10 | 344 | 354 | |
| Total | 88 | 368 | 456 | |
| Positive predictive value (95% CI) | Negative predictive value (95% CI) | Sensitivity (95% CI) | Specificity (95% CI) | Kappa (95% CI) |
| 0.76 (0.68–0.85) | 0.97 (0.96–0.99) | 0.89 (0.82–0.95) | 0.93 (0.91–0.96) | 0.77 (0.70–0.85) |
Definition of abbreviations: CI = confidence interval; DME = durable medical equipment.
Discussion
This study indicates that nearly one in five older Americans with COPD use supplemental oxygen, which was consistent across self-report and Medicare claims and a prior prevalence estimate (1). Although there is no true “gold standard” measurement for oxygen use, study results indicate reasonable concordance, sensitivity, and specificity between self-reported and Medicare claims for supplemental oxygen. Given the high degree of overlap, it is reasonable for researchers to use self-reported oxygen use in future studies.
Using self-reported supplemental oxygen can make population-based studies more feasible, as it can substantially increase sample sizes; self-report data do not require restricting the study to those who are 65 years or older and does not rely on fee-for-service Medicare-linked data (in our study, this more than halved our available sample). Furthermore, our results identify a novel cohort in the HRS that can be used to better describe the needs of persons with COPD using supplemental oxygen, including the impact of oxygen use on healthcare use and possible associations with accelerated geriatric syndromes.
Notably, a small number of participants (n = 24) self-reported supplemental oxygen use but lacked Medicare claims. We hypothesize that a small percentage of older adults obtain their own oxygen supplies (12), which might reflect either barriers to accessing Medicare-paid oxygen due to restrictive reimbursement policies or patients’ purchasing supplemental oxygen without medical indications (5, 10). Conversely, 10 of 88 participants with Medicare claims reported not using supplemental oxygen. Possible explanations include poor adherence to supplemental oxygen, non–COPD-related oxygen prescriptions, or short-term oxygen prescriptions after a hospitalization. Future work can be conducted to explore reasons for these small discrepancies, and when available, researchers should consider both self-report and claims data on oxygen use to ensure consistent results.
Strengths and Limitations
Our study has limitations. First, we could only determine COPD as the condition leading to self-reported oxygen use on the basis of the nested question design. This self-report method may miss supplemental oxygen use for other conditions such as heart disease or non-COPD lung disease, although Medicare claims might identify these individuals. Second, we relied on self-reported COPD and did not have pulmonary function testing or diagnostic codes to qualify the self-reported diagnosis. Third, we are unable to differentiate long-term from short-term oxygen use given the cross-sectional nature of this study. Future longitudinal studies are needed. Last, although the HRS uses complex survey weights to reliably derive national prevalence rates, there may be limitations in prevalence estimates for subgroups with small numbers.
Conclusions
We provide national prevalence estimates of supplemental oxygen use among persons with COPD. We demonstrate concordance between self-reported supplemental oxygen use and Medicare diagnostic codes, supporting the use of self-reported oxygen use for future population-based studies.
Footnotes
Supported by National Institute on Aging (NIA) grants T32AG000212 (A.O.S.), K76AG064327 (A.S.I.), K24AG068312 (A.S), and K23AG065438 (A.K.).
Author disclosures are available with the text of this letter at www.atsjournals.org.
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