Methodological considerations in evaluating post-AECOPD follow-up and long-term mortality

Dear Editor,

We read with great interest the recent article by Törölä et al., ‘Impact of a follow-up visit on two-year mortality after severe exacerbation of COPD in Finland’ published in the European Clinical Respiratory Journal [1]. The authors should be commended for conducting a large nationwide registry-based study investigating the relationship between post-exacerbation follow-up visits and long-term mortality among patients with severe acute exacerbation of chronic obstructive pulmonary disease (AECOPD). Their work provides valuable real-world evidence regarding healthcare utilization after severe exacerbations and highlights important prognostic factors associated with mortality.

One of the major strengths of this study is the use of comprehensive Finnish national healthcare registries with inclusion of over 63,000 COPD patients and adjustment for 23 explanatory variables. The authors also employed robust statistical methods, including conditional fixed-effects logistic regression and Cox proportional hazards sensitivity analysis, which improved the methodological rigor of the investigation. Furthermore, the identification of important mortality predictors such as older age, lung cancer, heart failure, renal failure, prolonged hospitalization, and readmission aligns with previous literature on COPD prognosis [2–4].

However, several methodological concerns deserve further discussion. The most important limitation appears to be residual confounding by indication. Patients referred for secondary-care follow-up were likely to have more severe disease, poorer functional status, and greater healthcare needs, factors that may not have been fully captured within administrative registry data. The observed association between secondary-care follow-up and increased mortality (OR 1.62, 95% CI 1.37–1.92) therefore may reflect baseline disease severity rather than a detrimental effect of follow-up itself. This interpretation is further supported by the sensitivity analysis in which the association lost statistical significance using a Cox proportional hazards model (HR 1.05, 95% CI 0.35–3.12). Such instability across statistical models raises concerns regarding the robustness of the findings.

Importantly, several clinically relevant variables known to influence COPD outcomes were unavailable in the registry database, including smoking status, lung function parameters (FEV1), arterial blood gas measurements, oxygen therapy requirements, body mass index, medication adherence, and use of non-invasive ventilation. Previous studies have demonstrated that these factors significantly influence mortality and exacerbation outcomes in COPD patients [5–7] Their absence may have resulted in incomplete adjustment for disease severity.

The study also highlights an important healthcare gap: only 23% of patients received any follow-up within 3 months after AECOPD despite guideline recommendations. This finding is concerning because post-exacerbation follow-up has been associated with reduced readmissions and improved continuity of care in several previous studies [8–10]. Early specialist or multidisciplinary follow-up may facilitate optimization of inhaled therapy, smoking cessation counseling, pulmonary rehabilitation referral, vaccination, and management of comorbidities, all of which contribute to improved patient outcomes [11].

Additionally, although mortality is an important endpoint, future studies should incorporate patient-centered outcomes such as quality of life, symptom burden, exercise tolerance, and hospital readmission rates. Mortality alone may underestimate the clinical benefits of structured COPD follow-up programs.

Overall, this study provides valuable nationwide epidemiological data and contributes meaningfully to the ongoing discussion regarding optimal post-AECOPD care pathways. Nevertheless, due to the limitations inherent in retrospective observational registry studies, caution is warranted before concluding that secondary-care follow-up is associated with worse outcomes. Prospective studies incorporating detailed clinical severity markers and standardized follow-up interventions are needed to better determine which COPD patients derive the greatest benefit from specialist versus primary-care follow-up.

Funding Statement

No funding was received for the preparation of this manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Ethical statement

Ethical approval not required,as this letter is based on a appraisal of previously published literature and did not involve human participants.