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. 2012 Nov 15;143(5):1430–1435. doi: 10.1378/chest.12-0354

Table 1.

—Classification and Grading Criteria for BO and BOS

Classification of BO Classification of BOS
C0: Biopsy sample absent of BO BOS 0: FEV1 > 90% of baseline  and FEF25%-75% > 75% of baseline
C1: Biopsy sample showing BO BOS 0-p: FEV1 81%-90%  of baseline and FEF25%-75% ≤ 75% of baseline
BOS 1: FEV1 66%-80% of  baseline
BOS 2: FEV1 51%-65%  of baseline
BOS 3: FEV1 ≤ 50% of baseline
Parameters for BO diagnosis Parameters for BOS diagnosis
 Presence defined by dense eosinophilic hyaline fibrosis in submucosa or bronchioles, resulting in partial or complete occlusion of lumina  Spirometry measurements made per ATS criteria
 Diagnosis requires at least five pieces of well-aerated lung parenchyma retrieved from biopsy  Baseline value defined as the average of the two highest posttransplant measurements obtained at least 3 wk apart without bronchodilators
 BOS is the preferred method for diagnosing chronic airway rejection  Changes present > 3 wk

Adapted from the guidelines of the International Society of Heart & Lung Transplantation.3,14 ATS = American Thoracic Society; BO = bronchiolitis obliterans; BOS = bronchiolitis obliterans syndrome; FEF25%-75% = forced expiratory flow, midexpiratory phase.