Serial ADAMTS13 measurements during initial plasma exchange therapy guide decisions for management of unresponsive thrombotic thrombocytopenic purpura

BACKGROUND The standard therapy in acquired thrombotic thrombocytopenic purpura (TTP) is plasma exchange. In unresponsive TTP, intensification of plasma exchange and immunomodulatory therapy can be initiated but it can be complicated to select for patients that will benefit from intensification. CASE REPORT We describe two cases of newly diagnosed TTP with a complicated clinical course during initial treatment with plasma exchange. In one case, after an initial response to plasma exchange, a decrease in platelet count was observed on Day 7. The normalized ADAMTS13 activity guided the clinicians in the diagnosis of a concurrent heparin‐induced thrombocytopenia due to the heparin lock, used for the indwelling catheter. The other case with TTP clinically deteriorated early during initial treatment. Reevaluation on Day 5, including ADAMTS13 activity, which was undetectably low, supported the clinical decision to intensify the plasma exchange to twice daily and start with the immunomodulating agent rituximab. In both clinically complicated cases measurements of ADAMTS13 activity during plasma exchange proved to be useful in guiding treatment decisions. CONCLUSION Serial measurements of ADAMTS13 activity should be considered in patients with newly diagnosed TTP with an unpredictable clinical course during initial therapeutic plasma exchange. These measurements may provide pivotal clinical insights on appropriate patient management.