Challenges and Pitfalls of Using Repeat Spirometry Recordings in Routine Primary Care Data to Measure FEV1 Decline in a COPD Population

Abstract

Background: Electronic healthcare records (EHR) are increasingly used in epidemiological studies but are often viewed as lacking quality compared to randomised control trials and prospective cohorts. Studies of patients with chronic obstructive pulmonary disease (COPD) often use the rate of forced expiratory volume in 1 second (FEV 1 ) decline as an outcome; however, its definition and robustness in EHR have not been investigated. We aimed to investigate how the rate of FEV 1 decline differs by the criteria used in an EHR database. Methods: Clinical Practice Research Datalink and Hospital Episode Statistics were used. Patient populations were defined using 8 sets of criteria around repeated FEV 1 measurements. At a minimum, patients had a diagnosis of COPD, were ≥35 years old, were current or ex-smokers, and had data recorded from 2004. FEV 1 measurements recorded during follow-up were identified. Thereafter, eight populations were defined based on criteria around: i) the exclusion of patients or individual measurements with potential measurement error; ii) minimum number of FEV 1 measurements; iii) minimum time interval between measurements; iv) specific timing of measurements; v) minimum follow-up time; and vi) the use of linked data. For each population, the rate of FEV 1 decline was estimated using mixed linear regression. Results: For 7/8 patient populations, rates of FEV 1 decline (age and sex adjusted) were similar and ranged from −18.7mL/year (95% CI −19.2 to −18.2) to −16.5mL/year (95% CI −17.3 to −15.7). Rates of FEV 1 decline in populations that excluded patients with potential measurement error ranged from −79.4mL/year (95% CI −80.7 to −78.2) to −46.8mL/year (95% CI −47.6 to −46.0). Conclusion: FEV 1 decline remained similar in a COPD population regardless of number of FEV 1 measurements, time intervals between measurements, follow-up period, exclusion of specific FEV 1 measurements, and linkage to HES. However, exclusion of individuals with questionable data led to selection bias and faster rates of decline.

A Harmonised Approach to Curating Research-Ready Datasets for Asthma, Chronic Obstructive Pulmonary Disease (COPD) and Interstitial Lung Disease (ILD) in England, Wales and Scotland Using Clinical Practice Research Datalink (CPRD), Secure Anonymised Information Linkage (SAIL) Databank and DataLoch

“…For COPD, we created a longitudinal record of forced expiratory volume in one second (FEV1) in litres (L) and FEV1% predicted (%) values, restricted to the ranges presented in Table S2 based on previous published research such as, 28 with additional columns denoting whether bronchodilation (if any) occurred before or after the spirometry test along with the Global Initiative for Obstructive Lung Disease (GOLD) staging of the value. Details of spirometry data cleaning can be found in Figure S5 .…”

“…Given low levels of reported post-bronchodilation measurements (7.2% of all FEV percent predicted measurements in CPRD; 5.7% in SAIL; 0.2% in DataLoch), GOLD stage was pragmatically reported using all available FEV percent predicted measurements in line with previous research that excluding those with more questionable data can lead to selection bias. 28 …”