Spirometry around the time of COPD diagnosis is associated with a reduced risk of COPD-related hospital admission or death from any cause in adults who had COPD diagnosed in the ambulatory setting

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Reference - CMAJ 2017 Apr 10;189(14):E530

• Guidelines recommend that chronic obstructive pulmonary disease (COPD) diagnosis be confirmed with spirometry, but evidence on its effect on morbidity and mortality is lacking.
• A retrospective cohort study assessed the clinical benefit of peridiagnostic spirometry in almost 69,000 adults in Ontario, Canada from 2005 to 2012.
• Peridiagnostic spirometry was associated with a reduced risk of COPD-related hospital admission or death from any cause (adjusted hazard ratio 0.91, 95% CI 0.89-0.94). In subgroup analyses, the risk was reduced in patients with COPD diagnosed during ambulatory visits, but not for patients with COPD diagnosed during in-patient hospitalization.

COPD guidelines recommend that airflow limitation in symptomatic patients be confirmed with spirometry (GOLD 2017, Ann Intern Med. 2011 Aug 2;155(3):179-91). Spirometry at diagnosis can also help to direct therapy. Despite recommendations, spirometry is not always used when diagnosing COPD (Chest 2014 Feb;145(2):272, Chest 2007 Aug;132(2):403, Respir Med 2010 Apr;104(4):550). One reason may be that evidence on the effect of spirometry for COPD diagnosis on morbidity and mortality is lacking. To address this deficit, a recent retrospective cohort study in Ontario, Canada used national databases to assess the clinical benefit of peridiagnostic spirometry, defined as spirometry conducted before or after bronchodilation beginning 1 year before the earliest COPD-related health service visit to the date of COPD diagnosis. The study included 68,898 adults (mean age about 69 years old) with physician-diagnosed COPD between 2005 and 2012, where physician-diagnosed COPD was defined as age ≥ 35 years plus either ≥ 1 COPD-related hospital admission or ≥ 3 COPD-related ambulatory care visits within 2 years of each other. Peridiagnostic spirometry was conducted in 41.2% of the population and was associated with differences in most baseline characteristics, including younger age (mean 67 vs. 70 years old), greater likelihood of specialist and guideline-based care, and lower likelihood of comorbidities. Risk analyses for clinical outcomes were adjusted for propensity scores (the probability, based on many demographic and clinical baseline characteristics, that a patient would have peridiagnostic spirometry) and spirometry before or after the peridiagnostic period.

The primary outcome of COPD-related hospital admission or death from any cause was observed in about 38% of the patients. In adjusted analyses of the entire study population, peridiagnostic spirometry was associated with a reduced risk of the primary outcome (adjusted hazard ratio [HR] 0.91, 95% CI 0.89-0.94). In subgroup analyses, the risk was reduced in patients with COPD diagnosed during ambulatory visits, but not for patients with COPD diagnosed during in-patient hospitalization. In patients ≥ 67 years old, for whom data on medication use for 2 years before COPD diagnosis was available, peridiagnostic spirometry was associated with an increased likelihood of new COPD-related prescriptions. In these patients, extending adjustments to include medication use eliminated the effects of spirometry.

This population-based retrospective cohort study demonstrated that spirometry around the time of COPD diagnosis was associated with a modest reduced risk of COPD-related hospital admission or death from any cause in adults who had COPD diagnosed in the ambulatory setting. The retrospective observational study design limits conclusions regarding the causative effect of peridiagnostic spirometry on outcomes. However, the use of propensity scores (which take into account many baseline demographic and clinical factors) and other factors to adjust risk analyses, and subgroup analyses, increases confidence that spirometry for diagnosis may be beneficial and enables speculation regarding how it may be beneficial. For example, the pathway by which spirometry benefits patients may be that it helps direct medication selection, a finding that agrees with an earlier study (Eur Respir J 2006 Nov;28(5):945). Regardless of the possible mechanisms, this study provides the best evidence to date in support of guideline recommendations to confirm COPD diagnosis with spirometry in symptomatic patients.

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