Can the intra-test variability of the single breath transfer factor of carbon monoxide method (TLCOsb) be improved to less than 5%?

Introduction: TL COsb is a key indicator of disease progression in Interstitial lung disease and other respiratory disease influencing management decisions including timing of referral for lung transplantation and in assessing prognosis. The current ATS/ERS and BTS/ARTP criteria stipulate at least two technically acceptable measurements within 10% or 1.0 mmol min -1 kPa -1 ; whichever is greater (MacIntyre et al., 2005; BTS/ARTP, 1994). This perceived lack of reproducibility limits the value of the test as a clinical tool: greater than 15% change is considered necessary for clinically significance (BTS guidelines: Thorax 2008;65). Aims and Objectives: This study assessed intra-test variance of the TL COsb measurement in a pulmonary function laboratory in a provincial general hospital to determine whether the introduction of more stringent reproducibility guidelines is practicable. Methods: Indices of TL COsb reproducibility were analysed from a sample of 452 patients referred for pulmonary function testing in Newport Chest Clinic, Newport. Results: 100% of the subjects met the current criteria. The mean CV (Coefficient of Variation) between repeated measurements was 1.5% (±2.5%). 406 patients (89.8%) achieved two measurements within 5% of the highest. Patient factors such as age, gender and BMI were not associated with measurement variability. Conclusion: Reproducibility of TL COsb can be better than current guidelines suggest. The introduction of more stringent criteria may improve the value of this test in the assessment of respiratory disease.