Study Backs Recommended Spirometry Cutoff for COPD Diagnosis

Veronica Hackethal, MD

June 26, 2019

The guideline-recommended FEV1:FVC value of less than 0.70 is the optimal cutoff for the diagnosis of clinically significant chronic obstructive pulmonary disease (COPD), researchers say.

The study, by Elizabeth C. Oelsner, MD, MPH, Columbia University Medical Center, New York City, and colleagues, was published online June 25 in JAMA.

FEV1:FVC, or the ratio of forced expiratory volume (the amount of air exhaled) in the first second to forced vital capacity (the total amount of air exhaled), is measured using spirometry. The ratio is used to evaluate airflow obstruction in the diagnosis of COPD.

"For clinicians, our study supports continued use of the currently recommended, fixed threshold of 0.70 for diagnosis of COPD. Our work supports the prognostic accuracy of spirometry — a noninvasive, cost-effective, reliable breathing test — for diagnosing airflow obstruction in COPD," Oelsner told Medscape Medical News.

Results from the study suggest that in the US population, an FEV1/FVC cutoff of 0.70 can predict COPD-related hospitalization and death with accuracy similar to that of an optimal cutoff and better than that of the lower limit of normal (LLN) of lung function.

The results have the potential to standardize and improve COPD diagnosis and care. Although spirometry is a relatively simple clinical tool, it is not used routinely to evaluate symptomatic individuals.

A number of professional guidelines — including those from the Global Strategy for the Diagnosis, Management, and Prevention of Chronic Obstructive Lung Disease (GOLD), NICE, the American College of Physicians, the American College of Chest Physicians, the American Thoracic Society, and the European Respiratory Society — recommend an FEV1:FVC of less than 0.70 for the diagnosis of COPD.

However, these recommendations are controversial. They are mainly based on expert opinion and lack research evidence to support them.

Other approaches can be used for diagnosing airflow obstruction. These fall into two main categories. The first bases the diagnosis of COPD on an FEV1:FVC cutoff that is less than the LLN, as determined from population data. The second uses a fixed FEV1:FVC cutoff, such as the 0.70 threshold. Other fixed cutoffs exist, such as those from the Global Lung Function Initiative and the Third National Health and Nutrition Examination Survey (NHANES III).

Depending on the approach, the prevalence of airflow obstruction can vary widely, as much as 33%, the authors explain. For a condition that affects 24 million people in the United States and ranks as the third leading cause of death worldwide, that can make a big difference in diagnosis and care.

In a linked editorial, Jørgen Vestbo, DMSc, University of Manchester, United Kingdom, and Peter Lange, DMSc, Copenhagen University, Denmark, discuss several potential drawbacks of these methods.

For example, the fixed cutoff is not adjusted for normal variation in lung function on the basis of age, sex, race, or height. The LLN approach adjusts for these variables, which may decrease bias. However, doing so may be irrelevant for diagnosing symptomatic individuals with risk factors for COPD, especially smokers, they write.

Also, a fixed FEV1:FVC cutoff does not take into account body mass index and may lead to underdiagnosis of obese individuals. A fixed FEV1:FVC cutoff may not accurately detect early COPD or concomitant mild emphysema. In addition, FEV1:FVC measurement can vary widely in the same individual over time, so repeat measurements are needed.

"[I]n an age of precision medicine and hope of pathway-driven treatments, it does not make sense to diagnose a disease based on a simple physiological measurement," they say.

Although results from the current study provide better evidence for the prognostic value of the FEV1:FVC < 0.70 cutoff, further research is needed to identify better biomarkers and characterize subtypes for a condition such as COPD that has broad a range of causes, they suggest.

They conclude, "While waiting, clinicians may be best advised to continue to use an old simple measurement, FEV1:FVC of less than 0.70, as an indicator of this complex disorder."

"[W]e completely agree that more work is needed to improve diagnosis and care for COPD — indeed, facilitating future research was a major motivation for this work," Oelsner agreed.

Oelsner's team is "very interested" in new ways to define subtypes of COPD. Imaging and genomics may be particularly promising, she added.

"Nonetheless, in clinical practice, it remains very important to have simple, noninvasive, cost-effective approaches to stratify risk and determine which patients require further evaluation or treatment. We anticipate that spirometry will continue to play an important role in this regard," she concluded.

The study is the National Heart Lung and Blood Institute (NHLBI) Pooled Cohort Study. Researchers analyzed pooled data from four large, multiethnic, population-based studies in the United States: the Atherosclerosis Risk in Communities Study; the Cardiovascular Health Study; the Health, Aging, and the Body Composition Study; and the Multi-Ethnic Study of Atherosclerosis.

The analysis included 24,207 participants aged 45 to 102 years (mean age, 63 years; 54% [n = 12,990] women; 69% [n = 16,794] non-Hispanic white; 24% [n = 5900] non-Hispanic black; and 63% [n = 15,181] ever smokers).

The researchers defined airflow obstruction using FEV1:FVC values ranging from 0.75 to 0.65, or LLN using the Global Lung Initiative reference equations (lowest fifth percentile of a healthy reference group, adjusted for age, sex, race, and height).

They used the Harrell C statistic, which assesses how well-predicted outcomes correlate to actual outcomes, to compare the accuracy of these cutoffs for the primary outcome, a composite of COPD-related hospitalization and mortality.

Seventy-seven percent of participants (n = 11,077) completed follow-up at 15 years.

During this time, 3925 participants experienced COPD-related events, including 3563 COPD-related hospitalizations and 447 COPD-related deaths.

The optimal cutoff for predicting COPD-related events was FEV1:FVC of 0.71 (C statistic, 0.696).

However, results for the 0.70 cutoff were not significantly different from the optimal 0.71 cutoff (0.67; C statistic difference, 0.001; 95% confidence interval [CI], −0.002 to 0.004; P = .54)

In contrast, the LLN cutoff was significantly less accurate than the optimal 0.71 cutoff (difference, 0.034; 95% CI, 0.028 – 0.041; P < .001).

Compared with the LLN, the 0.70 cutoff had lower specificity (79% vs 88%) and higher sensitivity (66% vs 49%).

Analyses adjusted for age, sex, race, height, study site, and cohort suggested that the optimal FEV1:FVC was 0.70 in ever smokers. This result is important because smokers constitute the majority of individuals with COPD.

The authors mention several potential study limitations. The study used prebronchodilator spirometry data, whereas guidelines recommend using postbronchodilator results. How that may have affected results is unknown. Also, the study used a single FEV1:FVC measurement, which may have missed individuals whose values varied over time. Finally, restricting the primary outcome to COPD-related hospitalization and death may have missed individuals with mild to moderate disease.

The study was supported by the National Institutes of Health. The original article contains a full listing of the authors' relevant financial relationships. Vestbo has received grants from Boehringer Ingelheim and personal fees from GlaxoSmithKline, Chiesi Pharmaceuticals, Boehringer Ingelheim, Novartis, and AstraZeneca.

JAMA. Published online June 25, 2019. Abstract, Editorial

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