 TTP is due to a decrease in an enzyme, ADAMTS 13 that is released by cells lining blood vessels endothelial cells. ADAMTS 13 cleaves or breaks down very large von Willebrand Factor vWF strands. vWF is used in blood clotting. Deficiency or inhibition of the enzyme, results in release of the ultra large vWF into the circulation. Platelets bind to these ultra large vWF multimers, promoting blood clot formation and platelet consumption thrombocytopenia. In more then 70 of TTP cases no precipitating cause can be found and the majority of these patients have antibodies against ADAMTS 13. Plasma Exchange PEX was introduced in the management of TTP in 1977 and the mortality of TTP patients has since decreased from approximately 90 to 15-20. PEX is essential in TTP treatment as plasma contains the missing enzyme ADAMTS 13. 