Bronchoalveolar lavage for supporting acute cellular rejection in lung transplant recipients: A retrospective...

Early detection of acute cellular rejection (ACR) is vital for improving long-term outcomes in lung transplant recipients (LTRs). Transbronchial biopsies are the gold standard for diagnosing ACR, but bronchoalveolar lavage (BAL) offers a less invasive alternative for early detection. This study examines the cytological and microbiological features of BAL, its correlation with ACR diagnosed via transbronchial cryobiopsy, and compares the effectiveness of pathology and hematology methods in analyzing BAL samples. Additionally, it assesses the value of mucosal biopsies for ACR detection.

Transbronchial biopsies and corresponding BALs from January 2020 to March 2024 were analyzed retrospectively. ACR was diagnosed using cryobiopsy according to ISHLT histopathological criteria. Associations between BAL parameters and ACR were assessed using mixed-effects analysis.

Among 240 procedures from 143 LTR, 17.9% were diagnosed with ACR. Microbiological findings and mucosal biopsy analyses were not associated with ACR. In contrast, the relative lymphocyte counts in BAL (median 3% [IQR 2-5%]) was significantly associated with ACR (OR 1.07 [95% CI 1.02-1.12], p=0.004). A significant correlation between lymphocyte proportion and ACR severity was observed (r=0.385, p<0.001). A threshold of 5.7% lymphocytes achieved an ROC AUC of 0.715 (95% CI 0.613-0.817), with a positive predictive value of 66.7% and a negative predictive value of 76.5%.

BAL lymphocytosis could support the diagnostic process of ACR. While mucosal biopsies and microbiological testing did not aid in ACR detection, BAL cytology provided relevant accuracy, particularly when assessed microscopically. These findings support incorporating BAL lymphocyte analysis into routine surveillance strategies for early ACR.