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 ≥ LLN_black but < LLN_white had 48% increased rate of breathlessness and almost doubled mortality, compared to blacks ≥ LLN_white. 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.