Proposal of a diagnostic algorithm for pediatric secondary ITP and non-IT. Red flags (or risk factors) are defined as female sex, age >10 years, moderate thrombocytopenia >20 × 10⁹/L, positive family history, comorbidities, and nonresponse to first-line treatment. CMV, cytomegalovirus; EBV, Epstein-Barr virus; HCV, hepatitis C virus.