Diffusing capacity ‘strongly predicted’ mortality in COPD patients

Key takeaways:

• All-cause mortality in COPD patients was “strongly predicted” by diffusing capacity of the lung for carbon monoxide, researchers wrote.
• Diffusing capacity had a similar measure of discriminative accuracy to the BODE index.

In patients with COPD, diffusing capacity of the lungs for carbon monoxide, or DLCO, was a predictor of mortality, according to study results published in Annals of the American Thoracic Society.

Further, compared with the BODE (BMI, obstruction, dyspnea and exercise capacity) index, which is frequently used to gauge the risk for mortality in COPD, DLCO showed comparable discriminative accuracy, according to researchers.

Meredith C. McCormack

“As we continue to strive to define new biomarkers in our understanding of disease and prognosis, this study demonstrated that a physiologic measurement that is simple and widely available was strongly associated with the risk of death among individuals with COPD,” Meredith C. McCormack, MD, MHS, associate director of the division of pulmonary and critical care medicine at Johns Hopkins University, told Healio. “DLCO performed similarly to the BODE index, which is a multidimensional score that incorporates several different assessments of disease severity in COPD.”

In time-to-event survival analyses, McCormack and colleagues analyzed 2,329 former or current smokers with COPD from the COPDGene Study to find out if DLCO could predict mortality.

To be included, patients had to have at least a 10-pack-year smoking history, an FEV₁/FVC ratio of less than 0.7 and DLCO measurements.

Researchers adjusted for age, sex, pack-years, smoking status, BODE index, CT percent emphysema (low attenuation areas below 950 Hounsfield units), CT airway wall thickness, history of cardiovascular disease and history of kidney disease in Cox proportional hazard models when evaluating survival.

Additionally, to assess the accuracy of DLCO percent predicted scores against BODE scores, researchers used C statistics.

Within the median follow-up period of 4.9 years, 393 patients (mean age, 71 years; 39% women; 22% African American) died.

Researchers found that DLCO predicted mortality (HR = 1.37; 95% CI, 1.29-1.44) in unadjusted models. Other predictors from these models included age, sex, BMI, pack-years, FEV₁ percent predicted, total percent emphysema, airway wall thickness, cardiovascular comorbidities and chronic kidney disease.

In these models, researchers also observed that declines in DLCO less than 70% predicted (mild diffusing capacity impairment) were linked to mortality.

After adjusting for various factors, researchers found that mortality went up 28% with every 10% decrease in DLCO percent predicted (adjusted HR = 1.28; 95% CI, 1.17-1.41). Other predictors from these models included FEV₁ percent predicted, age, sex, smoking status, airway wall thickness and chronic kidney disease, according to researchers.

Researchers continued to see DLCO percent predicted as an independent predictor of mortality even after the BODE index was introduced into this analysis.

“DLCO is a reflection of the lung's ability to exchange gases and is a simple, inexpensive test that can often be obtained at the same time as spirometry,” McCormack told Healio. “DLCO adds information that is unique and improves our ability to predict survival. Even mild impairments were found to be meaningful, and these findings suggest that DLCO is a clinical tool that may be useful in caring for patients with COPD.”

Further, DLCO percent predicted showed comparable accuracy to BODE (C statistic, DLCO = 0.68; BODE = 0.7) and had a greater C statistic than FEV₁ percent predicted, CT emphysema and CT airway wall thickness, according to researchers. With BODE plus DLCO, discriminative accuracy was found to increase (C statistic, 0.71).

“Future studies that shed light on the mechanisms that lead to DLCO abnormalities and increase risk for mortality are important next steps,” McCormack told Healio. “Additionally, studies that track DLCO over time and investigate how changes in DLCO are related to patient outcomes will be important to define our approaches in clinical care.”

For more information:

Meredith C. McCormack, MD, MHS, can be reached at mmccor16@jhmi.edu.