ADAMTS13 and antiphospholipid syndrome: Rituximab, discussed above, has been used with increasing frequency for the treatment of various hematologic and rheumatologic disorders including idiopathic TTP,171–173 acquired coagulation factor inhibitors,174,175 antiphospholipid antibody syndrome,173 systemic lupus erythematosus176 and rheumatoid arthritis.177,178 Rituximab use in relapsed, refractory TTP is linked to its ability to eliminate antibodies to ADAMTS13.171 Au et al.179 treated five TA-TMA patients refractory to a week of plasma exchange and prednisolone with rituximab 375mg/m2/week for four doses.