Etiologies and sequelae of extreme thrombocytosis in a large pediatric hospital

Extreme thrombocytosis (ET, platelet count >1000 × 103/ul) is an uncommon clinical finding 1. Primary ET is associated with myeloproliferative disorders, such as essential thrombocythemia 2. Secondary ET is more common and occurs in reaction to infection, inflammation, or iron deficiency. Bleeding and thrombotic complications more frequently arise in primary ET cases 1, but have been reported with secondary ET in adults 3. Etiologies and complications associated with ET in children are less well-defined, as prior pediatric studies have been relatively small or restricted to specialized patient populations 4,5. We aimed to characterize ET in a large, single-center pediatric cohort. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This work was supported by a grant from the National Institutes of Health, USA (T32HD043021 to CST), an American Academy of Pediatrics Marshall Klaus Neonatal-Perinatal Research Award (CST), and the Childre’s Hospital of Philadelphia Division of Neonatology. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Date: May 01, 2020 To: John Flibotte CC: Christopher Thom From: The Committees for the Protection of Human Subjects (IRB) Re: IRB 20-017443, Protocol Title: Evaluating causes and syndromes associated with extreme pediatric thrombocytosis (extremey high platelet counts). Sponsor or Funder: Children’s Hospital of Philadelphia, The (CHOP) IRB SUBMISSION: EXEMPTION GRANTED All necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes De-identified summary data will be made available upon request.