Refractory immune thrombocytopenia in adults: Towards a new definition

Immune thrombocytopenia (ITP) is an autoimmune haematological disorder characterized by immune-mediated thrombocytopenia and a variable risk of bleeding. Despite the availability of multiple treatment options, some patients are considered refractory since they do not achieve a platelet count response to multiple treatments and are at risk of bleeding. The term 'refractory' has been used to identify this patient group; however, with the advent of multiple lines of treatment, its meaning has become ambiguous. To address this issue, we reviewed previous definitions of refractory ITP, solicited the views of ITP experts and collected data from registries to inform a definition. Twenty ITP experts who attended the 7th Expert Meeting of the Intercontinental Cooperative ITP Study Group in September 2022 answered a web-based survey: 95% felt that there was a need for a new definition of refractory ITP for clinical and research purposes. The use of the term refractory, accompanied by a clear indication of the type and timing of failed treatments, was supported by 85% of respondents. Preliminary data on the frequency of refractory patients from the McMaster and Norwegian ITP Registries demonstrated that the proportion of adult ITP patients who had failed first-line therapy, rituximab, thrombopoietin receptor agonists, any immune suppressant medication and splenectomy ranged from 0.4% to 3.8%. We propose a definition of refractory ITP that could be evaluated in future studies.