COVID-19 and the liver - Lessons learned.

Liver involvement, indicated by elevated liver function test results, is common in hospitalized patients with coronavirus disease 2019 (COVID-19) and has been linked to disease severity and outcome. A dual pattern of elevated liver function tests can be observed especially in patients with severe or critical COVID-19, characterized by an increase in aminotransferases early in the course of this disease, followed by an increase in cholestasis-associated biochemistry markers at later stages. This dual pattern is associated with inflammatory response markers and poor outcome. Current notions on the mechanisms of liver injury in COVID-19 include direct cytopathic effects of the virus on hepatocytes and cholangiocytes, ischemic and hypoxic liver damage, drug-induced liver injury, activation of hepatic immune cells by excess cytokine production and exacerbation of pre-existing liver disease. Patients with obesity-related non-alcoholic fatty liver disease and, in particular, patients with cirrhosis are at high risk of liver injury and a fatal outcome from COVID-19. In contrast, individuals receiving stable immunosuppressive medication for autoimmune liver diseases or during long-term follow-up after liver transplantation do not have a higher case-to-infection ratio and have a fairly favourable outcome. The present review describes the epidemiology, characteristics and potential pathological mechanisms of COVID-19-related liver injury. Moreover, the influence of pre-existing liver disease on the susceptibility and severity of liver injury in COVID-19 are discussed.