The interpretation of platelet counts has to be revaluated in the light of caplacizumab. By effectively blocking platelet binding sites on VWF-multimers, the nanobody leads to a rapid normalization of the platelet count within 3 to 4 days. Most importantly, caplacizumab uncouples platelet counts from ADAMTS13 activity and thereby launches unprecedented thrombocyte dynamics, with potential pitfalls for over- and undertreatment.

A relevant number of patients responds to caplacizumab with a brisk increase in platelet count, followed by a marked dip of platelets (patient on the left). This may mislead treating physicians into re-intensifying therapy, with a respective risk for adverse side-effects and complications. Taken together, these observations call for reliable descriptions and the identification of predictive parameters to predict the platelet response upon administration of caplacizumab in a large patient cohort. Here, PREDICT-2020 is designed as a retrospective study to specifically address the following aspects:

• Identifying and describing clusters of platelet responses to caplacizumab
• Identifying potential pitfalls for treating physicians
• Predicting the individual thrombocyte response
• Correlating platelet responses with individual patient outcome

Inclusion Criteria:

• Confirmed diagnosis of autoimmune thrombotic thrombocytopenic purpura
• Treatment with at least a single dose of caplacizumab, either i.v. or s.c.
• Male or female patients older than 18 years of age

Exclusion Criteria:

• Hereditary thrombotic thrombocytopenic purpura

In this trial will be enclosed iTTP patients treated with caplacizumab from:

• the German real-world cohort of iTTP patients treated with caplacizumab in the years 2018 to 2020 , and
• the respective TITAN and HERCULES trial cohorts.