https://orcid.org/0000-0002-7926-1945
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Abstract
Introduction
Clinical decisions in chronic obstructive pulmonary disease (COPD) treatment often utilize serially assessed physiologic parameters and biomarkers. To better understand the reliability of these tests, we evaluated changes in commonly assessed biomarkers over 3 months in patients with clinically stable COPD.
Methods
We performed an observational prospective cohort study of 89 individuals with clinically stable COPD, defined as no exacerbation history within 3 months of enrollment. Biomarkers included lung function and functional performance status, patient-reported outcomes of symptoms and health status, and blood markers of inflammation. The correlation between testing at baseline and at 3-month follow-up was reported as the intraclass correlation coefficient (ICC). “Outliers” had significant variability between tests, defined as >1.645 standard deviations between the two measurements. Differences in clinical features between outliers and others were compared.
Results
Participants with COPD (n = 89) were 70.5 ± 6.7 years old, 54 (61%) male, had a 40 pack-year smoking history with 24.7% being current smokers, and postbronchodilator forced expiratory volume in one second (FEV1) 62.3 ± 22.7% predicted. The biomarkers with excellent agreement between the initial and the follow-up measurements were FEV1 (ICC = 0.96), Saint George’s Respiratory Questionnaire (SGRQ) (ICC = 0.98), COPD Assessment Test (CAT) (ICC = 0.93) and C-reactive protein (CRP) (ICC = 0.90). By contrast, parameters showing less robust agreement were 6-minute walking distance (ICC = 0.75), eosinophil count (ICC = 0.77), erythrocyte sedimentation rate (ICC = 0.75) and white blood cell count (ICC = 0.48). Individuals with greater variability in biomarkers reported chronic bronchitis more often and had higher baseline SGRQ and CAT scores.
Conclusion
Our study evaluated the stability of commonly assessed biomarkers in clinically stable COPD and showed excellent agreement between baseline and three-month follow-up values for FEV1, SGRQ, CAT and CRP. Individuals with chronic bronchitis and more symptomatic disease at baseline demonstrated greater variability in 3-month interval biomarkers.
Conclusions
In a prospective study of the longitudinal variability of commonly assessed biomarkers in clinically stable COPD, we showed fair to excellent agreement between baseline and three-month follow-up values, with FEV1, SGRQ, CAT and CRP being the most stable measures, while the six-minute walk test, leukocyte counts and ESR were more variable over the three-month period. Consistent variability in both subjective patient-reported outcomes and objective measures of lung function and inflammation was characteristic of more advanced COPD. Further studies are needed to better understand possible associations of instability of these biomarkers with clinical outcomes.
Data Sharing Statement
The data that support the findings of this study are available from the corresponding author, upon reasonable request.
Ethics Approval and Informed Consent
This study was approved by the UCLA Institutional Review Board (IRB# IRB 14-000748) and was performed in compliance with the Declaration of Helsinki. Written informed consent was obtained from all participants.
Author Contributions
All authors made a significant contribution to the work reported, whether that is in the conception, study design, execution, acquisition of data, analysis and interpretation, or in all these areas; took part in drafting, revising or critically reviewing the article; gave final approval of the version to be published; have agreed on the journal to which the article has been submitted; and agree to be accountable for all aspects of the work.
Disclosure
JP is an employee of Amgen Inc. CBC reports personal fees from PulmonX, GlaxoSmithKline, NUVAIRA and MGC Diagnostics, outside the submitted work. DPT has consulted with AstraZeneca, Sunovion, Mylan and Theravance. IZB has consulted with Astra Zeneca, Grifols, Verona Pharma, Sanofi, Theravance, Viatris, Aerogen and Inhibrx and has received research grants from AMGEN, Aerogen, Theravance and Viatris and GE Healthcare. RGB reports personal fees from Viatris/Theravance Biopharma, outside the submitted work. The authors report no other conflicts of interest in this work.