Lung clearance index (LCI) as a sensitive marker of post-transplant bronchiolitis obliterans syndrome (BOS)

Introduction: Long term outcomes after lung transplant (LTx) are limited by the development of BOS. BOS is defined by the International Society of Heart and Lung Transplantation (ISHLT) as an irretrievable drop in FEV1 below 80% of the best FEV1 post-LTx. HRCT is used to confirm spirometric findings. LCI is a sensitive measure of small airways changes that may identify those with early disease. Aim: To measure LCI in LTx patients and compare with ISHLT and CT grades for BOS. Methods: LCI was measured at routine clinic review in stable double LTx recipients using a closed circuit Innocor device and SF6 washout on room air. BOS grades were derived from serial spirometry and (where available) HRCT according to ISHLT criteria. Results: 30 patients were assessed (15 M), mean (SD) age: 51 (13.8) yrs; time since LTx: 3.5 (2.8) yrs [range 0.3-11.3]. LTx indications were CF (n=7), COPD (13), pulmonary hypertension (6), ILD (4). 22(73%) met ISHLT BOS definitions (≥BOS-0p). LCI in those with BOS grades 2-3 (n=4, mean LCI=15.1) was significantly higher than those with no BOS (n=8, LCI=7.3), BOS-0p (n=12, LCI=8.4) and BOS-1(n=6, LCI=9.3), p 7) but preserved FEV1(>80%). Conclusion: LCI can be successfully measured in LTx patients, and changes with BOS grade. Longitudinal assessments will reveal whether abnormal LCI in those with preserved FEV1 predicts future clinical change.