Table 3– Grading (staging) of bronchiolitis obliterans syndrome (BOS)#
BOS GradeSpirometry % of baseline
1993 Classification2002 Classification
0FEV1 ≥80%FEV1 >90% and FEF25–75% >75%
0-p+Not includedFEV1 81–90% and/or FEF25–75% ≤75%
1FEV1 66–80%FEV1 66–80%
2FEV1 51–65%FEV1 51–65%
3FEV1 ≤50%FEV1 ≤50%

  • FEV1: forced expiratory volume in 1 s; FEF25–75%: forced expiratory flow at 25–75% of forced vital capacity. #: Other causes of lung function decline must be excluded (e.g. acute rejection, infection, native lung problems for single lung recipients, excessive recipient weight gain, anastomotic dysfunction, respiratory muscle dysfunction, effusion, or technical problems such as erroneous measurements due to device dysfunction); : baseline is defined as the average of the two best FEV1 (or FEF25–75%) values (≥3 weeks apart) following functional recovery and stabilisation post-lung transplantation; +: in Grade (stage) 0-p the “p” denotes “probable” early BOS and is used to indicate 10–20% decline in baseline FEV1 that is likely due to an early stage of BOS that does not meet criteria for BOS Grade 1.