Chronic rejection is not well understood, even by lung transplant patients. But I recently came across a good explanation and I’ve reproduced it here. It’s an article titled What is Chronic Rejection? from the most recent newsletter sent out by my lung transplant clinic at the University of Colorado:
The diagnosis of chronic rejection can be made in two ways: a lung tissue biopsy or changes in breathing tests (also called pulmonary function tests or spirometry). Chronic rejection in a lung tissue biopsy is defined by scarring or fibrosis in the small airways. This finding is a “histological diagnosis” made by looking at the tissue under a microscope. The scarring will obliterate the airways (also called bronchioles) and thus the process is called obliterans bronchiolitis or bronchiolitis obliterans. Generally the biopsies obtained during a bronchoscopy are too small to make a diagnosis of obliterans bronchiolitis. A larger lung biopsy can be done in the operating room, but this requires intubation, general anesthesia and a hospital stay so it is not routinely done.
Because of the complications and risks of an operating room lung biopsy, patients and physicians have sought a way to define chronic rejection by breathing tests. As the small airways become scarred and fibrotic with chronic rejection, there is a decline in breathing tests. This decline is called BOS.
BOS reflects a clinical diagnosis of chronic rejection. BOS is graded by severity of decline in breathing test numbers. Specifically, we look at the forced expiratory volume in one second or FEV1. After transplant, the FEV1 may be low but will gradually increase over time (months to even years after transplant). The highest FEV1 after transplant becomes that patient’s baseline FEV1. Future FEV1 measurements are compared to this baseline. Progressive decline in the ratio of the current FEV1 to the baseline FEV1 defines the stages of BOS.
It is important to note that many factors can decrease the FEV1 besides chronic rejection. Most notably, infection and acute rejection can decrease the FEV1. However, in these situations, the FEV1 should increase with treatment of the infection or acute rejection. Decline in the FEV1 that is permanent and irreversible defines BOS.
A few notes. First, BOS stands for Bronchiolitis Obliterans Syndrome. Second, I’ve never had the operating room lung biopsy they mention but I’ve had many bronchoscopies. The bronchoscopy is a very common procedure for lung transplant patients. They sedate you and then send a scope down into your lungs, sometimes snipping a little biopsy while down there. The procedure is used to check the lungs for infection and rejection. Third, when I talk about my lung capacity I’m talking about my FEV1.