A diagnosis of TTP is based on the clinical symptoms with the concomitant presence of thrombocytopenia (platelet count below 100×109/L) and microangiopathic hemolytic anemia with schistocytes on the blood smear, a negative direct antiglobulin test (Coombs test), elevated levels of hemolysis markers (such as total bilirubin, LDH, free hemoglobin, and an unmeasurable haptoglobin), after exclusion of any other apparent cause. USS can present similar to the following diseases, which have to be excluded: fulminant infections, disseminated intravascular coagulation, autoimmune hemolytic anemia, Evans syndrome, the typical and atypical form of hemolytic uremic syndrome, HELLP (hemolysis, elevated liver enzymes, low platelets) syndrome, pre-eclampsia, heparin-induced thrombocytopenia, cancer that is often accompanied with metastasis, kidney injury, antiphospholipid antibody syndrome, and side effects from hematopoietic stem cell transplantation. Of note is that pregnancy associated affections like pre-eclampsia, eclampsia, and HELLP syndrome can overlap in their presentation as pregnancy can trigger TTP episodes. Patients with fulminant infections, disseminated intravascular coagulation, HELLP syndrome, pancreatitis, liver disease, and other active inflammatory conditions may have reduced ADAMTS13 activity, but almost never a relevant severe ADAMTS13 deficiency <10% of the normal. A severe ADAMTS13 deficiency below 5% or <10% of the normal (depending on the definitions) is highly specific for the diagnosis of TTP. ADAMTS13 activity assays are based on the direct or indirect measurement of VWF-cleavage products. Its activity should be measured in blood samples taken before therapy has started, to prevent false high ADAMTS13 activity. If a severe ADAMTS13 deficiency is present an ADAMTS13 inhibitor assay is needed to distinguish between the acquired, autoantibody-mediated and the congenital form of TTP (USS). The presence of antibodies can be tested by ELISA or functional inhibitor assays. The level of ADAMTS13 inhibitor may be fluctuating over the course of disease and depends on free circulatory antibodies, therefore a onetime negative test result does not always exclude the presence of ADAMTS13 inhibitors and thereby an autoimmune origin of TTP. A severe ADAMTS13 deficiency in the absence of an inhibitor, confirmed on a second time point in a healthy episode of a possible USS patient, usually sets the trigger to perform a molecular analysis of the ADAMTS13 gene to confirm a mutation. In unclear cases a plasma infusion trial can be done, showing an USS in the absence of anti-ADAMTS13-antibodies a full recovery of infused plasma-ADAMTS13 activity as well as a plasma half-life of infused ADAMTS13 activity of 2–4 days. A deficiency of ADAMTS13 activity in first-degree relatives is also a very strong indicator for an<unk> .
Upshaw–Schulman syndrome
Haglund's syndrome
Potocki–Shaffer syndrome
Frey's syndrome
Perlman syndrome
Urethral syndrome
Lamb-Shaffer syndrome
Shone's syndrome