{
  "abstract": "Background Forced expiratory volume in 1 s (FEV 1) and forced vital capacity (FVC) are two of the most common measurements in spirometry, which are used for the diagnosis and monitoring of respiratory disease. Within-individual variation in measured FEV1 and FVC may affect their clinical utility but estimates of this are based on limited and often poor-quality data.Methods A retrospective cohort study was performed. Data on FEV 1 and FVC results and sociodemographic, lifestyle and comorbidity covariates were extracted from the IQVIA Medical Research Database. A minimum of four measurements in the same individual within a 6-month time period from the first measurement was the only inclusion criterion. Within-individual measured variation was calculated as a coefficient of variation (CV) using a linear regression random effects model using within-subject variance to estimate CV for the whole population and various subgroups.Results 4412 participants for FEV 1 and 3567 participants for FVC were included in the main study. The mean number of measurements per individual in the 6-month period was 4.8 (SD 2.3) for FEV1 and 5.1 (SD 3.5) for FVC. The overall CV for FEV1 was 22.4% (95% CI 22.1% to 22.8%) and for FVC was 15.2% (95% CI 15.0% to 15.5%). This is much higher than seen in a previous systematic review of spirometry variation. CV increased as mean patient FEV1 and FVC decreased.Conclusions Estimated within-individual variation in this analysis of real-world data is much higher than previously reported. Variation increases with more severe disease status. This has important implications for diagnosis, monitoring and clinical decision-making.",
  "authors": [
    {
      "affiliations": [
        "Department of Applied Health Sciences, University of Birmingham, Birmingham, UK"
      ],
      "name": "Alex Gough"
    },
    {
      "affiliations": [
        "Department of Applied Health Sciences, University of Birmingham, Birmingham, UK"
      ],
      "name": "Tom Marshall"
    },
    {
      "affiliations": [
        "Department of Applied Health Sciences, University of Birmingham, Birmingham, UK",
        "Birmingham Biomedical Research Centre, National Institute for Health and Care Research, London, UK"
      ],
      "name": "Alice M Turner"
    },
    {
      "affiliations": [
        "Department of Applied Health Sciences, University of Birmingham, Birmingham, UK",
        "Birmingham Biomedical Research Centre, National Institute for Health and Care Research, Birmingham, UK"
      ],
      "name": "Alice Sitch"
    }
  ],
  "title": "Within-individual variation of spirometry measurements in primary care: a retrospective cohort study",
  "uid": "615961d1-8c9c-5a0b-aa81-d20acedf8e0d"
}