*2.2.1 Bronchoalveolar lavage (BAL) and transbronchial biopsy (TBB)*

Bronchoscopic techniques have been employed in the evaluation of pulmonary sarcoidosis for a very long time and have been the mainstay of histological confirmation historically. Granulomatous inflammation in sarcoidosis usually involves the bronchovascular and centrilobular structures.

Transbronchial biopsies help to obtain the histological diagnosis in support of clinical-radiological diagnosis especially when the superficial mucosal or cutaneous lesions are not amenable for sampling [13, 14]. The diagnostic sensitivity of TBB in the diagnosis of a broad spectrum of interstitial lung diseases (ILDs) ranges from 29 to 79% [15–19]. The British Thoracic Society Sarcoidosis Registry data has previously showed that transbronchial biopsies have lesser diagnostic yield than EBUS-TBNA [20].

Bronchoalveolar lavage findings supportive of sarcoidosis include predominant lymphocytosis on differential cell count analysis along with CD4/CD8 lymphocyte ratio of more than 1. Müller-Quernheim et al. demonstrated that inflammation is compartmentalized in sarcoidosis resulting in lymphocyte abundance in the involved organs [21]. In a study by Prasse et al., patients with sarcoidosis had higher expression of IL2, IFN gamma, and TNF alpha [22]. Furthermore, Tanriverdi et al. showed that high CD4/CD8 ratio, though specific is not a sensitive test for the diagnosis of sarcoidosis, and therefore, it does require clinico-radiological and pathological correlation [23]. BAL lymphocytosis of ≥40% in the appropriate clinical context would support the diagnosis of hypersensitivity pneumonitis or cellular nonspecific interstitial pneumonia (NSIP) over sarcoidosis [24]. However, bronchoalveolar lavage findings in isolation are unlikely to help establish the diagnosis of sarcoidosis.
