26th June 2023

Haemolytic uraemic syndrome

Haemolytic uraemic syndrome (HUS) is characterised by a thrombotic microangiopathy which causes damage to the endothelial cells of blood vessels. It causes anaemia and thrombocytopenia due to intravascular haemolysis.

The common features of HUS are:

• Anaemia
• Thrombocytopenia
• Raised unconjugated bilirubin
• Raised lactate dehydrogenase (LDH)
• Decreased circulating levels of haptoglobin
• Reticulocytosis

The microvasculature of the kidney is most affected in HUS, with the involvement of other organs only occurring in more severe cases. The most common cause of classical HUS is infection with E coli O 157 and its enterotoxin. This typically causes a diarrhoeal illness and is the most common cause of AKI in children in the developed world. This is referred to as D+HUS. The severe diarrhoea associated with HUS often leads to intravascular depletion due to dehydration and, therefore, a pre-renal acute kidney injury. There is good spontaneous recovery in most patients, but sometimes renal replacement therapy is required. In 10% of cases, no infective cause is identified, and this is called atypical HUS. Atypical HUS is subclassified into familial and sporadic subtypes and is associated with dysregulation of the complement system leading to thrombotic microangiopathy.