Research race-specific reference values and lung function impairment, breathlessness and prognosis: Analysis of NHANES 2007-2012

Background: Spirometry reference values differ by race/ethnicity, which is controversial. We evaluated the effect of race-specific references on prevalence of lung function impairment and its relation to breathlessness and mortality in the US population. Methods: Population-based analysis of the National Health and Nutrition Examination Survey (NHANES) 2007-2012. Race/ethnicity was analyzed as black, white, or other. Reference values for forced expiratory volume in one second (FEV1) and forced vital capacity (FVC) were calculated for each person using the Global Lung Initiative (GLI)-2012 equations for (1) white; (2) black; and (3) other/mixed people. Outcomes were prevalence of lung function impairment (< lower limit of normal [LLN]), moderate/severe impairment (< 50%pred); exertional breathlessness; and mortality until 31 December, 2015. Results: We studied 14,123 people (50% female). Compared to those for white, black reference values identified markedly fewer cases of lung function impairment (FEV1) both in black people (9.3% vs. 36.9%) and other non-white (1.5% vs. 9.5%); and prevalence of moderate/severe impairment was approximately halved. Outcomes by impairment differed by reference used: white (best), other/mixed (intermediate), and black (worst outcomes). Black people with FEV1 >= LLNblack but < LLNwhite had 48% increased rate of breathlessness and almost doubled mortality, compared to blacks >= LLNwhite. White references identified people with good outcomes similarly in black and white people. Findings were similar for FEV1 and FVC. Conclusion: Compared to using a common reference (for white) across the population, race-specific spirometry references did not improve prediction of breathlessness and prognosis, and may misclassify lung function as normal despite worse outcomes in black people.