Unit | Calculation formula | Recommendation | |
Absolute volume change# (ΔFEV1) | Litres (L) or millilitres (mL) | post-bronchodilator FEV1 – initial FEV1 | ATS 1991 [3], ERS 1993 [4], ATS/ERS 2005 [5], GINA 2002–2007 [6], BTS/SIGN 2008–2016 [13], NICE 2017 [14] |
ΔFEV1 % of the initial FEV1 | Percentage (%) | (post-bronchodilator FEV1-initial FEV1)/initial FEV1 × 100 | ACCP 1974 [15], Intermountain Thoracic Society 1984 [16], ATS 1991 [3], ATS/ERS 2005 [5], NHLBI 2007 [17], GINA 2002–2017 [6], BTS/SIGN 2008–2016 [13], NICE 2017 [14] |
ΔFEV1 % predicted¶ | Percentage (%) | (post-bronchodilator FEV1 − initial FEV1)/predicted FEV1 × 100 | ERS 1993 [4], NHLBI 2007 [17], GPIAG 2009 [18] |
ATS: American Thoracic Society; ERS: European Respiratory Society; GINA: Global Initiative for Asthma; BTS: British Thoracic Society; SIGN: Scottish Intercollegiate Guidelines Network; NICE: National Institute for Health and Care Excellence; ACCP: American College of Chest Physicians; NHLBI: National Heart, Lung, and Blood Institute; GPIAG: General Practice Airways Group. #: absolute volume change is usually combined with the percentage change cut-off. Only in BTS/SIGN guidelines was a single cut-off value based on the absolute change used as a criterion. ¶: can also be expressed as post-bronchodilator FEV1% pred – pre-bronchodilator FEV1% predicted.