Thrombotic
thrombocytopenia purpura (
TTP) is a rare, life-threatening disease with an incidence of approximately 2 persons per million per year. It is characterized by severe deficiency of the von Willebrand cleaving
protease, ADAMTS13 (a
disintegrin and
metalloproteinase with a
thrombospondin type 1 motif, member 13), leading to formation of platelet-rich thrombi in the microvasculature. Prompt initiation of appropriate
therapy, particularly
plasma exchange, may be life-saving. Diagnosis of
TTP is challenging because of its diverse clinical manifestations, overlap in clinical presentation with other
thrombotic microangiopathies, and limited availability of ADAMTS13 testing. Clinical prediction scores have been developed to estimate the pretest probability of severe ADAMTS13 deficiency and may be used as an adjunct to clinical judgment to guide initial management decisions. An ADAMTS13 activity level of less than 10% supports the diagnosis of
TTP in appropriate clinical contexts, but many centers do not offer testing in-house and must send out the test to a reference laboratory with a turnaround time of several days. In such instances, initial management decisions must be made without the benefit of laboratory testing. In patients with
TTP, inhibitor tests may be useful for distinguishing immune-mediated from congenital
TTP. In this article, we review the epidemiology, natural history, and clinical presentation of
TTP and laboratory assays for
TTP including ADAMTS13 activity and inhibitor assays. We also describe an evidence-based approach to the evaluation of a patient with suspected
TTP that integrates clinical and laboratory assessment.