Conceptual algorithm. The algorithm depicted conceptually describes our approach to the treatment of patients presenting with an acute TMA. PEX is started initially in all patients, with the response to PEX serving as an important diagnostic criterion. Collectively, the pretreatment ADAMTS13, platelet count, serum creatinine, and the response to PEX are used to clinically differentiate acquired TTP from aHUS. After recovery, complement mutation studies may be useful to confirm the clinical diagnosis in cases where a complement protein mutation (CFH, CFI, C3, CFB, THBD, or MCP) is present.