Efficacy of different plasma sources in the treatment of thrombotic thrombocytopenic purpura

Abstract

Plasma exchange (PE) with fresh frozen plasma (FFP) is the treatment of choice for thrombotic thrombocytopenic purpura (TTP). Since TTP patients are exposed to a large number of plasma donors, they would benefit from any additional measure of plasma safety. Several such measures have been implemented but doubts remain as to whether the new types of plasma are as effective as FFP or whether some plasma fraction may be more effective. Cryoprecipitate‐poor plasma (CCP) was introduced in the therapeutics of TTP as a superior alternative to FFP. However, a clinical trial by the Canadian Apheresis Group failed to confirm the therapeutic superiority of CPP over FFP. Quarantine FFP (qFFP) is as effective as chemically modified plasma in the prevention of HIV, HBV and HCV transmission. Since qFFP has not been chemically manipulated, it must be regarded as equivalent to FFP both in terms of protein composition and therapeutic efficacy. Solvent/detergent (SD) plasma has long been used in the treatment of TTP and seems to be as effective as FFP. However, the only formal proof of efficacy consist in a small trial involving only 26 patients. Methylene blue‐photoinactivated plasma (MBPIP) is used in some regions in Spain and other European countries. A recent multicentric, ‘quasi experimental’ trial involving 102 cases of idiopathic TTP has shown that MBPIP is less effective than qFFP. Patient in the MBPIP arm required twice as many PE procedures and more adjuvant therapies to achieve remission and had a higher risk of TTP recrudescence. There is only one randomized trial comparing psoralen‐photoinactivated plasma to FFP. Though no difference was found in the rate of TTP remission, the trial recruited only 35 patients and was therefore severely underpowered. Levels of ADAMTS13 activity, as measured by the current laboratory assays, are similar in the various plasma sources despite some (i.e. MBPIP) are clinically less effective. In conclusion, FFP and qFFP are the plasma sources of choice for PE in TTP. CPP is probably as effective as FFP. MBPIP should be avoided because it is less effective. There is no proof that SD‐plasma and psoralen‐photoinactivated plasma are therapeutically equivalent to FFP. Normal levels of ADAMTS13 in therapeutic plasma seem not to be an accurate proxy of clinical effectiveness.