The role of bronchoalveolar lavage in diagnosis and prognosis of COVID-19 patients

SARS-CoV-2 infection diagnosis is mainly based on nasopharyngeal swab real-time reverse-transcriptase-polymerase reaction positivity in the presence of clinical and radiological suspicion of viral infection. In case of negative test, bronchoscopy with bronchoalveolar lavage (BAL) is the most used technique to rule out SARS-CoV-2 infection. The role of BAL in COVID-19 diagnosis is debated since its diagnostic yield is highly influenced by several factors. Nevertheless, the analysis of BAL fluid provides many important information about the COVID-19 alveolar environment. The analysis of alveolar populations, as well as cytokines and chemokine production, may contribute to better understand the pathogenetic mechanisms involved in COVID-19, providing information on patients’ prognosis. Moreover, many efforts have been spent on transcriptome analysis of host response to SARS-CoV-2 infection. In this narrative review we explored the role of BAL in diagnosis and prognosis of patients with COVID-19, focusing on its diagnostic yield, on its role in the study of alveolar cytology, cytokines and chemokines production, microbiological coinfection and how they can influence the prognosis of COVID-19 patients.