All-Trans Retinoic Acid (ATRA) Combining Dexamethasone Versus High-dose Dexamethasone for Initial Treatment of Primary Immune Thrombocytopenia (ITP)

Inclusion Criteria: 1. Meet the diagnostic criteria for immune thrombocytopenia. 2. Untreated hospitalized patients, may be male or female, between the ages of 18 \~ 80 years. 3. To show a platelet count \< 30×10\^9/L, and with bleeding manifestations. 4. Eastern Cooperative Oncology Group（ECOG）performance status ≤ 2. 5. Willing and able to sign written informed consent Exclusion Criteria: 1. Received chemotherapy or anticoagulants or other drugs affecting the platelet counts within 3 months before the screening visit. 2. Received high-dose steroids or \[2\] intravenous immunoglobulin transfusion(IVIG)in the 3 weeks prior to the start of the study. 3. Current HIV infection or hepatitis B virus or hepatitis C virus infections. Severe medical condition (lung, hepatic or renal disorder) other than ITP. 4.Unstable or uncontrolled disease or condition related to or impacting cardiac function (e.g., unstable angina, congestive heart failure, uncontrolled hypertension or cardiac arrhythmia) 5.Female patients who are nursing or pregnant, who may be pregnant, or who contemplate pregnancy during the study period. 6.Have a known diagnosis of other autoimmune diseases, established in the medical history and laboratory findings with positive results for the determination of antinuclear antibodies, anti-cardiolipin antibodies, lupus anticoagulant or direct Coombs test. 7.Patients who are deemed unsuitable for the study by the investigator.