Alternative methods have been proposed to report spirometry indices from test sessions (forced expiratory volume 1 s, FEV1; forced vital capacity, FVC). However, most use the American and European Societies’ standard (ATS/ERS) which stops sessions once a repeatability threshold is met which may not accurately represent intra-session variability. Our goal was to repeat trials beyond the repeatability threshold and evaluate alternative reporting methods. 130 adults performed spirometry across two visits. Spirometry indices were reported using the ATS/ERS standard and four alternatives. 78 participants (60%) had valid data for all methods and visits. Intra-session coefficients of variation were low (FEV1: 3.1–3.7%; FVC: 2.3–2.8%). Our four alternative methods yielded FEV1 and FVC values ≤ 0.08 L different from ATS/ERS standard, which is not clinically meaningful. Intraclass correlation coefficients were ≥ 0.97 indicating consistency across repeated measures. The smallest real differences ranged from FEV1: 0.20–0.27 L and FVC: 0.18–0.24 L indicating consistency and low measurement error. Overall, all methods for reporting FEV1 and FVC demonstrated similar measurement error, precision, and stability within- and between-visits. These results suggest that once ATS/ERS repeatability is achieved, which approach is used for reporting spirometric variables may be of low clinical significance in a healthy population.

Forced oscillation technique (FOT) provides unique information on respiratory system mechanical properties complementing pulmonary function testing. However, a lack of evidence guiding acquisition/reporting of parameters has slowed clinical FOT adoption. Current European Respiratory Society (ERS) standards recommend 3–5 trials per session comprising three trials with a coefficient of variation (CoV) ≤ 10% for low-frequency resistance. We present an analysis of different combinations of trial selection methods and session validity thresholding variables (low- and mid-frequency resistance and reactance [R5, R19, X5], low-frequency reactance area [AX] and tidal volume) comparing proportion of subjects achieving valid data across two test sessions (7 ± 3 days apart) and within and between session measurement variabilities. 126 (98%) subjects achieved valid data across both sessions (2666 trials). With R5 or R19 as criteria and selection of any three trials from ≥ 4 attempts, ≥ 75% of subjects achieved validity. Furthermore, with R5 or R19 criteria and selection of any trials from ≥ 5 attempts, CoVs for resistance outcomes were reduced within session while variabilities of FOT outcomes between sessions remained consistent. Within session differences in measurement variabilities were not clinically meaningful. Our analyses support current ERS reporting recommendations for healthy adults. Future work should apply this analytic approach to patient populations.

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