Inclusion Criteria:  1.18 years or older 2.Primary ITP 3.Failed initial glucocorticosteroid treatment, 4.Applying rhTPO or Eltrombopag as subsequent treatment 5.Switch from rh-TPO to eltrombopag or vice versa 6.Normal neutrophils 7.Available follow-up at least 6 weeks after switching  Exclusion Criteria:  HIV positive status, or active infection of HBV or HCV Suffering from a serious or progressive disease, which, in the investigator's judgment, put the subject at undue risk for participation in this study (i.e. cancer or pre-cancer, immunocompromised, uncontrolled diabetes, epilepsy, severe cardio-cerebrovascular disease(s) (i.e. stroke, idiopathic aortic stenosis, aneurysm, hypertrophic obstructive cardiomyopathy, ischaemic heart disease, tachyarrhythmias, severe heart failure [classified as NYHA III-IV], severe lung dysfunctions, etc)) History of thrombosis plus two or more risk factors as defined in Caprini thrombosis risk assessment model Lactating or pregnant women, or WOCBP who are unwilling to use highly effective contraceptive measures during the study period Abnormal liver and renal functions: AST or ALT or total bilirubin ≥1.5 × ULN, and/or creatinine ≥176.8 μmol/L Women of childbearing potential (WOCBP) that are pregnant or wish to become pregnant during the prospective phase of the study. Other conditions which the investigator considers inappropriate for enrollment