Patients with a baseline DLCO (diffusing capacity for carbon monoxide) of < 60% of predicted have more severe disease clinical expression with higher mortality risk, according to a long-term observational study of Global Initiative for Obstructive Lung Disease (GOLD) I chronic obstructive pulmonary disease (COPD) patients. Clarifying mechanisms of low DLCO may help clinicians direct interventions toward ameliorating the low capacity, Juan Pablo de Torres, MD, and colleagues wrote in the journal CHEST®.
Defining increased risk
“Can a DLCO threshold help define an increased risk of death and a different clinical presentation in GOLD I patients?” the researchers questioned. For evaluation of COPD, the GOLD does not currently promote the use of DLCO, and the clinical and prognostic utility of a low DLCO has not been studied, the authors noted.
Several COPD studies, however, have shown associations between low DLCO values and reduced exercise capacity, increased symptoms, risk of severe exacerbations, and mortality. The patients included in these studies, however, have generally had moderate to severe airflow limitation, and have not had postbronchodilator forced expiratory volume in 1 second/forced vital capacity (FEV1/FVC) < 0.70 and an FEV1 ≥ 80%, defined by GOLD as COPD spirometric stage I. These mild obstruction GOLD I patients, in large epidemiological studies, do have increased risk of death. But it is often assumed, Dr. de Torres and colleagues noted, that “mild” suggests a good prognosis. They propose that a simple DLCO measurement could help identify those GOLD I patients with “worse overall COPD compromise and an increased risk of death.” Importantly, GOLD I represents the largest percentage of patients with airflow limitation that epidemiological studies have identified.
The researchers enrolled 360 GOLD stage I COPD patients, recording their age, sex, pack-years’ history, body mass index, dyspnea, lung function measurements, exercise capacity, BODE (body mass index, airflow obstruction, dyspnea, and exercise capacity) index, and history of exacerbations, and followed them for a mean of 109 months. They identified a cutoff DLCO value for all-cause mortality, compared the clinical and physiological characteristics of patients above and below the threshold, and explored the predictive power of that cutoff value.
All-cause mortality difference
The mean age in the overall population studied was 63 years (31% were women), with 43% active smokers, and pack-years history of 45. Overall mortality was 11% during the follow-up period. The predominantly male population was mildly overweight, had few comorbidities, normal FEV1 values, mild dyspnea, normal 6-minute walk distance, and very few exacerbations.
Analysis showed a DLCO cutoff value of < 60% was associated with a significant all-cause mortality differential (DLCO ≥ 60%: 9% vs. DLCO < 60%: 23%, P = .01). At a same FEV1% predicted and Charlson score, patients with DLCO < 60% had lower BMI, more dyspnea, lower inspiratory capacity (IC)/total lung capacity (TLC) ratio, lower 6-minute walk distance, and higher BODE index. Adjusted Cox multiple regression analysis confirmed that a DLCO < 60% was associated with an all-cause mortality hazard ratio [HR] of 3.37, (95% confidence interval, 1.35-8.39; P = .009).