New perspectives on the thrombotic complications of haemolysis

Summary Many clinical settings are associated with haemolysis, from rare conditions, such as paroxysmal nocturnal haemoglobinuria, to common interventions, such as mechanical circulatory support and blood transfusion. The toxic effects of circulating free haemoglobin, haem, and iron are becoming increasingly understood and include an increased risk of thrombotic complications. This review summarizes the epidemiological evidence for an association between haemolysis and thrombosis and explores potential underlying mechanisms. New insights into the role haem plays in inflammatory signalling and in generating neutrophil extracellular traps (NETs) may provide useful strategies for managing pathological states associated with severe haemolysis. A better understanding of the toxic effects of haemolysis will result in better therapies to prevent the side effect of thrombosis.