Association of Timely Spirometry With Lower All-Cause Mortality: A Nationwide Obstructive Cohort Study

Background: Although spirometry is the gold standard for diagnosing COPD, it is underused in clinical practice. Research Question: Which factors are associated with timely spirometry (at chronic treatment initiation) in a clinically relevant population of people starting chronic treatment for respiratory symptoms? Is this diagnostic test associated with lower mortality risk? Study Design and Methods: Incident adult users of chronic respiratory medication were identified in Belgian nationwide data. The odds on timely spirometry were examined by multivariable logistic regression and impact on survival by using multivariable Cox regression analysis. In those patients not receiving timely spirometry, factors related to further delay in spirometry were analyzed with a multivariable Fine-Gray subdistribution hazard regression. Results: Among 146,205 chronic treatment initiators, 20.9% had spirometry at treatment initiation, and 13.8% received spirometry during follow-up. Although primary care physicians prescribed 81.1% of initiated treatments, general practitioners performed only 5.1% of all spirometry tests. People who received spirometry at treatment initiation had a 34% lower mortality risk (adjusted hazard ratio, 0.66; 95% CI, 0.63-0.70) and had less use of short-acting bronchodilators. Smoking, respiratory morbidities, and congestive heart failure increased chance of spirometry use. In contrast, female sex, age < 60 years or > 80 years, cognitive impairment, and frailty lowered the chance of spirometry use, both at initiation and during follow-up. Low socioeconomic status, depression/anxiety, and antibiotic use were associated with a lower chance of spirometry use at treatment initiation, whereas during follow-up, antibiotic use was associated with a higher chance of spirometry over time. In addition, anemia and cachexia were associated with a lower chance of spirometry use during follow-up. Interpretation: Only 1 in 3 initiators of chronic treatment for obstructive lung disease underwent spirometry. Spirometry was particularly underused in primary care. Especially (never-smoking) female participants and vulnerable patients may be at increased risk for underdiagnosis and suboptimal treatment. Importantly, spirometry at treatment initiation was significantly associated with better prognosis, possibly through better-tailored care.