• Platelets are cells that aid in hemostasis at bleeding sites. They are primarily produced in the bone barrow and have an average life span of 7-10 days [1, 2].

  • The spleen normally stores 25% of the body’s platelets in reserves and can be released in times of adrenergic need [3].

  • Thrombocytopenia becomes more critical and often symptomatic when platelet counts are <50,000 per mcL [4].

Causes [4, 5]

Special Populations


Similar causes as for adults, but especially consider:

  • Immune thrombocytopenic purpura (ITP) [7]
    • Can occur at any age, but usually occurs at age 2-5 years old
    • Most common cause of acquired thrombocytopenia in children
  • Neonatal alloimmune thrombocytopenia [8]
    • When maternal antibodies cross the placenta and attach to fetal platelet antigens from father

Pregnancy [9, 10]

The mean platelet count is slightly lower during pregnancy, with <1% of normal pregnancies reporting a platelet count <100,000/mcL. Physiologic thrombocytopenia may occur because of sequestration and pooling the splenic and placental circulation.

  • Gestational thrombocytopenia
    • Occurs incidentally in 6% of pregnancies, usually near the time of delivery
    • Typically fall in the range of 100,000-150,000/mcL.
  • Pregnancy-induced immune-mediated thrombocytopenia (ITP)
  • Eclampsia
    • Typically occurs at 20+ weeks of gestation and can also occur post-partum
  • HELLP syndrome (hemolysis, elevated liver enzymes, low platelets)
    • Typically occurs at 20+ weeks of gestation but can also occur post-partum

Key Insights

Obtain a blood smear

Peripheral blood smears may help to differentiate the cause for thrombocytopenia by looking at the platelet size/shape as well as evaluate the other 2 hematologic cells lines (red and white cells) [4].

Perform a careful investigation of the patient's medications

Drug-induced immune thrombocytopenia has been associated with over 300 medications. Investigate the patient’s medication list in the setting of thrombocytopenia [11].

Associated with COVID infection severity

COVID infection severity has been linked with thrombocytopenia through multiple mechanisms [12]:

  • Bone marrow suppression
  • Pulmonary microthrombi cause increased platelet destruction
  • Platelet autoantibody formation

COVID vaccine complication

Vaccine-induced immune thrombotic thrombocytopenia (VITT) can occurs with non-mRNA-based COVID-19 vaccines, such as from Astra Zeneca and Johnson & Johnson [13].

  • Similar to heparin-induced thrombocytopenia
    • Similar pathophysiology being immune-mediated)
    • Hypercoagulable state
    • Occurs 5-10 days after COVID vaccine
  • Increased platelet consumption

Originally published Feb 16, 2023


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  2. Arnold DM, Lim W. A rational approach to the diagnosis and management of thrombocytopenia in the hospitalized patient. Semin Hematol. 2011;48(4):251-258. doi:10.1053/j.seminhematol.2011.08.002. PMID 22000090
  3. Kapila V, Wehrle CJ, Tuma F. Physiology, Spleen. [Updated 2022 May 8]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-.
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  6. Arepally GM, Cines DB. Pathogenesis of heparin-induced thrombocytopenia. Transl Res. 2020;225:131-140. doi:10.1016/j.trsl.2020.04.014. PMID 32417430[Open access full article]
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  8. Norton T, Newberry D, Jnah A. Neonatal Alloimmune Thrombocytopenia: A Concise Review. Adv Neonatal Care. 2021;21(2):115-121. doi:10.1097/ANC.0000000000000775. PMID 32657948
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  11. Bakchoul T, Marini I. Drug-associated thrombocytopenia. Hematology Am Soc Hematol Educ Program. 2018;2018(1):576-583. doi:10.1182/asheducation-2018.1.576. PMID 30504360
  12. Lippi G, Plebani M, Henry BM. Thrombocytopenia is associated with severe coronavirus disease 2019 (COVID-19) infections: A meta-analysis. Clin Chim Acta. 2020;506:145-148. doi:10.1016/j.cca.2020.03.022. PMID 32178975
  13. Aleem A, Nadeem AJ. Coronavirus (COVID-19) Vaccine-Induced Immune Thrombotic Thrombocytopenia (VITT) [Updated 2022 Oct 3]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-.
Michelle Lin, MD
ALiEM Founder and CEO
Professor and Digital Innovation Lab Director
Department of Emergency Medicine
University of California, San Francisco
Michelle Lin, MD


Professor of Emerg Med at UCSF-Zuckerberg SF General. ALiEM Founder @aliemteam #PostitPearls at https://t.co/50EapJORCa Bio: https://t.co/7v7cgJqNEn
Michelle Lin, MD