ADAMTS13 activity measurement is used in the diagnostic algorithm of thrombotic thrombocytopenic purpura (TTP), but results may not be available before initiation of therapeutic plasma exchange (TPE). The immature platelet fraction (%-IPF) and the calculated absolute immature platelet count (A-IPC) represent a test of real-time thrombopoiesis, and can be performed in most laboratories using automated analyzers. Here we report on using A-IPC kinetics to exclude idiopathic TTP in a patient with severe hypertension, thrombocytopenia, and acute renal failure, which was confirmed by a normal ADAMTS13. The complete resolution of thrombocytopenia occurred once blood pressure was controlled favoring a diagnosis of hypertension-induced thrombotic microangiopathy.
The initial description of therapeutic plasma exchange (TPE) in an animal model was published almost 100 years ago. Since that time, this treatment has been applied to a wide variety of diseases but limited research has been published examining the mechanisms of action of TPE. The therapeutic effects of TPE could include the removal of pathological substances from the blood, such as monoclonal paraproteins and autoantibodies, as well as the replacement of deficient plasma components when plasma is used as a replacement fluid. Beyond these potential mechanisms, other possible mechanisms include possible alterations in lymphocyte proliferation and function that could sensitize these cells to immunosuppressant and chemotherapeutic agents and alterations in the immune system including changes in B and T cell numbers and activation, increased T suppressor function, and alteration in T-helper cell type 1/2 (Th1/Th2) ratio. Much remains unknown about the mechanisms of action of TPE, indicating a need for basic research into this therapy.
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