Peking University People's Hospital is conducting a small prospective study looking at the effectiveness of using Zanubrutinib in adults with ITP between 18-70 years of age. They are looking to recruit 10 patients who live in China. Zanubrutinib is BTK kinase inhibitor that is currently used to treat refractory mantle cell lymphoma. Participants must have confirmed primary and refractory ITP (i.e., not responding to other ITP therapies), have a platelet count less than 30,000/μL or with bleeding symptoms. Exclusions include current treatment with chemotherapy or anticoagulants (“blood thinners”), infection with HIV or hepatitis B/C, or having cancer or other severe medical conditions. Pregnant (or nursing mothers) will be excluded from participating.