All patients with HUS associated with seasonal or epidemic influenza should undergo rapid testing for ADAMTS13 activity, plasma C3, global hemolytic capacity (CH50 and AH50), circulating MAC (sC5b-9) and anti-CFH antibodies, in addition to genetic studies targeting HUS-associated complement and coagulation factors (Fig. 3). The gene discussed is CFH; the disease is hemolytic-uremic syndrome.