aHUS for clinicians

What is aHUS?

Haemolytic uraemic syndrome (HUS) comprises the triad of microangiopathic haemolytic anaemia, thrombocytopaenia and acute kidney injury. Approximately 90% of cases are caused by Shiga-toxin producing bacteria, such as Escherichia coli O157 and are called STEC-HUS. The remainder of cases are called atypical haemolytic uraemic syndrome (aHUS).

aHUS is an ultra-rare disease, incidence is estimated at 0.4 per million per year and presents at all ages. aHUS can be classified into primary and secondary forms. Secondary forms of aHUS will be discussed later.

In cases of primary aHUS, at least half of patients are known to have an abnormality of regulation of the alternative pathway of complement that leads to dysregulation of complement at the endothelial surface – therefore many cases of primary aHUS are complement-mediated.


Patients with aHUS may have triggering event that is noted prior to presentation e.g. respiratory tract infections, other infections, malignancy, pregnancy etc. In addition, the presentation of aHUS may associate with extra-renal manifestations such as neurological involvement, pancreatic involvement and digital gangrene. Familial cases of aHUS have been reported.


The prognosis of patients with complement mediated aHUS historically was poor. The majority of patients progressed to end-stage renal failure and recurrent disease in renal transplants was common. The introduction of eculizumab, a monoclonal antibody against C5 controls disease in many patients and prevents the development of end-stage renal failure in individuals with complement mediated aHUS.