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, bron-choscopy 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 patho-genetic 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 influ-ence the prognosis of COVID-19 patients.