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.