{
  "abstract": "Introduction The British Thoracic Society (BTS) clinical statement on air travel (Coker et al. 2022; Thorax 77(4):329-350) provides a pre-flight assessment tool for patients with restrictive respiratory disease including those with interstitial lung disease (ILD) to determine the requirement for hypoxic challenge testing (HCT).A major determinant of HCT eligibility is a transfer factor for carbon monoxide (TLCO) of ≤50% predicted. Research investigating intersession variability in TLCO reported values can differ by 0.8375 (mmol.min.kpa) for results <50% predicted and 1.1725 (mmol.min.kpa) for ≥50% predicted (Yadav et al. 2025;Chest 0012-3692(25)05249-3).This audit aims to investigate the effect of TLCO variability on the recommendations for HCT in the ILD patient cohort at our centre.Methods A retrospective analysis was performed on TLCO data obtained from patients referred from the ILD service between 01/01/2025 to 30/01/2026. Inclusion criteria consisted of test quality in line with departmental standard operating procedures, a TLCO result with a Z-score < -1.645, and a 6-minute walk test with oxygen saturation nadir <95% measured by pulse oximetry. Patients diagnosed with airways obstruction were excluded from data analysis.TLCO values equal to 50.1% or ≤50% predicted were calculated, and compared to achieved TLCO value. Calculations were performed to determine what change in TLCO (mmol.min.kpa) was required in their achieved result to change their HCT eligibility. Global Lung Initiative (GLI) equations for TLCO % predicted were used (Stanojevic et al. 2017 Eur Respir J 50(3): 1700010).After running measurements of normal distribution, median and interquartile range were used for absolute values and % predicted values of TLCO.As this retrospective clinical audit will not require changing patient care from accepted standards, it was deemed that ethical approval was not required.Results The study population and results are summarised in table 1.Conclusions These results suggest an intersession variability in TLCO of 0.717 mmol.min.kpa would elicit a change in this population’s HCT pathway. This value is less than the intersession variability quoted by Yadav et al. In conclusion, those using the BTS statement to determine HCT requirement in ILD patients need to be mindful of the inherent intersession variability of TLCO.Abstract P59 Table 1",
  "authors": [
    {
      "affiliations": [
        "Royal Free London NHS Foundation Trust, London, United Kingdom"
      ],
      "name": "Joseph Burt"
    },
    {
      "affiliations": [
        "Royal Free London NHS Foundation Trust, London, United Kingdom"
      ],
      "name": "Brett Gregory"
    },
    {
      "affiliations": [
        "Royal Free London NHS Foundation Trust, London, United Kingdom"
      ],
      "name": "Katie Ward"
    }
  ],
  "title": "P59 Effect of intersession gas transfer variability on a hypoxic challenge testing pathway in interstitial lung disease patients",
  "uid": "701afa1c-39de-5dea-9485-997e325f5c1d"
}