A) Model of Ham test for PNH (top) and indirect Ham test for aHUS diagnosis (bottom). The Ham test evaluates the effect of acidified serum on patient's cells, whereas the modified test evaluates the effect of patient's serum on GPI-anchored protein–deficient reagent cells. Both tests use absorbance changes as readouts of cell viability. GPI-AP indicates glycosylphosphatidylinositol-anchored proteins. B) WST-1 cell viability assay in patients with aHUS. Percentage of nonviable reagent cells in aHUS after exposure to acute-phase serum, remission serum on eculizumab (Ecu), and remission serum off eculizumab compared with acute or remission serum from TTP patients.