Abstract
RATIONALE: Understanding factors associated with undiagnosed obstructive lung disease and its impact on mortality could inform the ongoing discussions about benefits and risks of screening and case finding. OBJECTIVES: To define factors associated with undiagnosed obstructive lung disease and its long-term mortality. METHODS: Cross-sectional analysis of participants, aged 20 to 79 years, in two National Health and Nutritional Examination Surveys (NHANES), NHANES III (1988-1994) and NHANES 2007-2012, with longitudinal follow-up of NHANES III participants. MEASUREMENTS AND MAIN RESULTS: We classified participants with spirometry-confirmed obstructive disease, based on the fixed ratio definition (FEV1/FVC < 0.7), as "diagnosed" (physician diagnosis of either asthma or chronic obstructive pulmonary disease), and "undiagnosed" (no recorded physician diagnosis). For the longitudinal analysis of NHANES III participants, mortality was the outcome of interest. We tested the contribution of self-reported health status and comorbidity burden (exposure) to the odds of being undiagnosed using logistic models adjusted for demographics, smoking status, and lung function. We estimated hazard ratios (HRs) for all-cause mortality for diagnosed and undiagnosed subjects participating in NHANES III who had spirometry using Cox- proportional regression analysis. Among those with spirometry-defined obstruction, 71.2% (SE, 1.8) in NHANES III and 72.0% (SE, 1.9) in NHANES 2007-2012 were undiagnosed. In multivariate models, undiagnosed obstructive disease was consistently associated in both surveys with self-reported good/excellent health status, lower comorbidity burden, higher lung function, and being of racial/ethnic minority. Among NHANES III participants (median follow up, 14.5 yr), both undiagnosed (HR, 1.23; 95% confidence interval, 1.08-1.40) and correctly diagnosed participants (HR, 1.74; 95% confidence interval, 1.45-2.09) had higher risk for all-cause mortality than participants without obstruction. CONCLUSIONS: Undiagnosed obstructive lung disease is common among American adults and remained unchanged over 2 decades. Although undiagnosed subjects appear healthier than those with a diagnosis, their risk of death was increased compared with subjects without obstruction. These findings need to be considered when judging the implications of case-finding programs for obstructive lung disease.