Race/Ethnicity and Reference Equations for Spirometry

Changes in Spirometry Interpretative Strategies: Implications for Classifying COPD and Predicting Exacerbations

BACKGROUND

Recent guidelines for spirometry interpretation recommend both race-neutral reference equations and use of z score thresholds to define severity of airflow obstruction.

RESEARCH QUESTION

How does the transition from race-specific to race-neutral equations impact severity classifications for patients with COPD when using % predicted vs z score thresholds, and do changes in severity correspond to clinical risk?

STUDY DESIGN AND METHODS

This retrospective cohort study included Black and White patients with COPD and available spirometry from the Johns Hopkins Health System. Global Lung Function Initiative (GLI) 2012 (race-specific) equations and GLI Global (race-neutral) equations were used to determine FEV1 % predicted and z score values. Patients were classified as having mild, moderate, or severe disease according to % predicted or z score thresholds. Associations between a change in severity classification from race-specific to race-neutral with COPD exacerbations and all-cause hospitalizations were evaluated using logistic regression.

RESULTS

This cohort included 13,324 patients, of whom 9,232 patients (69.3%) were White (mean age, 65.7 years) and 4,092 patients (30.7%) were Black (mean age, 61.1 years). More Black than White patients showed a change in severity classification between approaches when using % predicted thresholds (20.2% vs 6.1%; P < .001), but not with z score thresholds (12.6% vs 12.3%; P = .68). An increased severity classification with a race-neutral approach was associated with increased risk of exacerbation when using z score thresholds (OR, 2.34; 95% CI, 1.51-3.63), but not when using % predicted thresholds (OR, 1.08; 95% CI, 0.61-1.93). A decreased severity classification with a race-neutral approach was associated with lower risk of exacerbation with both % predicted (OR, 0.49; 95% CI, 0.28-0.87) and z score (OR 0.67; 95% CI, 0.50-0.90) thresholds.

INTERPRETATION

The proportions of Black and White individuals reclassified were similar with z score thresholds, and changes in severity corresponded to clinical risk with z scores. These results support recent recommendations for use of race-neutral equations and z score thresholds for spirometry interpretation.

FEV1Q: a race-neutral approach to assessing lung function

BACKGROUND

Forced expiratory volume in 1 s quotient (FEV1Q) is a simple approach to spirometry interpretation that compares measured lung function to a lower boundary. This study evaluated how well FEV1Q predicts survival compared with current interpretation methods and whether race impacts FEV1Q.

METHODS

White and Black adults with complete spirometry and mortality data from the National Health and Nutrition Examination Survey (NHANES) III and the United Network for Organ Sharing (UNOS) database for lung transplant referrals were included. FEV1Q was calculated as FEV1 divided by 0.4 L for females or 0.5 L for males. Cumulative distributions of FEV1 were compared across races. Cox proportional hazards models tested mortality risk from FEV1Q adjusting for age, sex, height, smoking, income and among UNOS individuals, referral diagnosis. Harrell's C-statistics were compared between absolute FEV1, FEV1Q, FEV1/height2, FEV1 z-scores and FEV1 % predicted. Analyses were stratified by race.

RESULTS

Among 7182 individuals from NHANES III and 7149 from UNOS, 1907 (27%) and 991 (14%), respectively, were Black. The lower boundary FEV1 values did not differ between Black and White individuals in either population (FEV1 first percentile difference ≤0.01 L; p>0.05). Decreasing FEV1Q was associated with increasing hazard ratio (HR) for mortality (NHANES III HR 1.33 (95% CI 1.28-1.39) and UNOS HR 1.18 (95% CI 1.12-1.23)). The associations were not confounded nor modified by race. Discriminative power was highest for FEV1Q compared with alternative FEV1 approaches in both Black and White individuals.

CONCLUSIONS

FEV1Q is an intuitive and simple race-neutral approach to interpreting FEV1 that predicts survival better than current alternative methods.

The Current State of Health Inequities in COPD

An understanding of the health inequities that surround the treatment and prevention of COPD is required to address the barriers that hinder improvement of care for underserved populations. This scoping review was conducted to identify the existing evidence of social factors that affect the health, health-care access, and health-care quality of patients with COPD within the United States, and to identify gaps in knowledge to help direct future research. We followed the guidelines from the Joanna Briggs Institute and Preferred Reporting Items for Systematic reviews and Meta Analyses Extension for Scoping Reviews. In July 2022, a literature search by using Ovid (Embase) and MEDLINE (PubMed) databases was conducted to identify articles on COPD, published between 2016 and 2021, written in English, and that investigated at least one health inequity as defined by the National Institutes of Health. All studies were screened for inclusion criteria and were extracted in a masked, duplicate manner. Each health inequity was investigated, extracted, and summarized. Thirty articles were screened in full text, and 19 were found to meet inclusion criteria. Common social factors investigated in the COPD literature included race/ethnicity, income, and education. Since the implementation of the National Institutes of Health's sex and gender minority category in 2016, only one study within our sample examined LGBTQ+ (lesbian, gay, bisexual, transgender, queer [or sometimes questioning], and others) patients with COPD. The least commonly investigated social factors that affect patients with COPD were rural/under-resourced (geography), sex and gender, and LGBTQ+ affiliation. In addition, occupational status was not investigated by any included studies in our sample. Our scoping review underlines the lack of research with regard to inequities that affect patients with COPD. We propose researching hormone replacement therapy's impact on lung function in transgender and nonbinary patients with COPD. Implementation science studies are suggested to enhance intervention for COPD medication adherence among racial/ethnic minority groups, given the intersectionalities of social factors that disproportionately affect this population. We, also recommend developing telemedicine pulmonary rehabilitation technology for rurally located patients with COPD.

Race-Specific Spirometry Equations Do Not Improve Models of Dyspnea and Quantitative Chest CT Phenotypes

BACKGROUND

Race-specific spirometry reference equations are used globally to interpret lung function for clinical, research, and occupational purposes, but inclusion of race is under scrutiny.

RESEARCH QUESTION

Does including self-identified race in spirometry reference equation formation improve the ability of predicted FEV1 values to explain quantitative chest CT abnormalities, dyspnea, or Global Initiative for Chronic Obstructive Lung Disease (GOLD) classification?

STUDY DESIGN AND METHODS

Using data from healthy adults who have never smoked in both the National Health and Nutrition Survey (2007-2012) and COPDGene study cohorts, race-neutral, race-free, and race-specific prediction equations were generated for FEV1. Using sensitivity/specificity, multivariable logistic regression, and random forest models, these equations were applied in a cross-sectional analysis to populations of individuals who currently smoke and individuals who formerly smoked to determine how they affected GOLD classification and the fit of models predicting quantitative chest CT phenotypes or dyspnea.

RESULTS

Race-specific equations showed no advantage relative to race-neutral or race-free equations in models of quantitative chest CT phenotypes or dyspnea. Race-neutral reference equations reclassified up to 19% of Black participants into more severe GOLD classes, while race-neutral/race-free equations may improve model fit for dyspnea symptoms relative to race-specific equations.

INTERPRETATION

Race-specific equations offered no advantage over race-neutral/race-free equations in three distinct explanatory models of dyspnea and chest CT scan abnormalities. Race-neutral/race-free reference equations may improve pulmonary disease diagnoses and treatment in populations highly vulnerable to lung disease.

Towards a Race-Neutral System of Pulmonary Function Test Results Interpretation

It has been observed widely that, on average, Black individuals in the United States have lower FVC than White individuals, which is thought to reflect a combination of genetic, environmental, and socioeconomic factors that are difficult to disentangle. Debate therefore persists even after the American Thoracic Society's 2023 guidelines recommending race-neutral pulmonary function test (PFT) result interpretation strategies. Advocates of race-based PFT results interpretation argue that it allows for more precise measurement and will minimize disease misclassification. In contrast, recent studies have shown that low lung function in Black patients has clinical consequences. Furthermore, the use of race-based algorithms in medicine in general is increasingly being questioned for its risk of perpetuating structural health care disparities. Given these concerns, we believe it is time to adopt a race-neutral approach, but note that more research is urgently needed to understand how race-neutral approaches impact PFT results interpretation, clinical decision-making, and patient outcomes. In this brief case-based discussion, we offer a few examples of how a race-neutral PFT results interpretation strategy will impact individuals from racial and ethnic minority groups at different scenarios and stages of life.