Due to the rarity of TTP, the infrequency of a complete TTP pentad, variable and atypical presentations, and overlap with other thrombotic microangiopathies (TMAs), diagnosis is difficult to achieve. The current approach is to determine a presumptive diagnosis based on clinical prediction tools (PLASMIC score) and ADAMTS13 activity. This evidence concerns the gene ADAMTS13 and thrombotic thrombocytopenic purpura.