• Clinical science

Thrombocytopenia (Low platelet count)


Thrombocytopenia is a platelet count below the normal range (< 150,000/mm3) that is most commonly due to impaired platelet production in the bone marrow or increased platelet turnover in the periphery. Common causes of impaired platelet production include bone marrow failure, infection, malignancy, and chemotherapy/radiation. Additional etiologies include hereditary syndromes, such as Wiskott-Aldrich syndrome and Alport syndrome. In contrast, increased peripheral platelet turnover may be caused by autoimmune conditions (e.g., immune thrombocytopenia), drugs (e.g., heparin), and other conditions (e.g., TTP/HUS, DIC/sepsis). Thrombocytopenia is often asymptomatic and found incidentally on routine bloodwork. Patients may notice petechiae or mucosal bleeding (e.g., bleeding gums, epistaxis) at lower platelet counts. Other patients with thrombocytopenia are clinically ill and have multisystem findings (e.g., acute infection, liver disease, TTP/HUS, DIC). Treatment depends on the underlying condition with observation sufficing for many patients who have stable medium-low platelet levels, or corticosteroids in those with lower platelet counts.


Impaired platelet production in bone marrow

Bone marrow conditions → megakaryocytesthrombopoiesis

If platelet production is impaired, the number of megakaryocytes on bone marrow biopsy will also be decreased!

Increased platelet turnover in the periphery

Increased peripheral turnover also increases numbers of megakaryocytes on bone marrow biopsy!

Redistribution, dilution, and other causes


Clinical features

Clinical features according to platelet count
Platelet count/mm3 Symptoms
> 150,000
  • Normal/asymptomatic
  • Typically no abnormal bleeding, i.e., asymptomatic thrombocytopenia
  • Often asymptomatic, prolonged bleeding may occur following trauma or surgery
  • Prolonged bleeding following trauma or surgery are more likely; scattered petechiae, rarely purpura
< 5,000
  • Hematologic emergency



A rapidly falling platelet count is a cause for concern, even if it is within the normal range (e.g., in HIT).


  • Treat the underlying cause [7]
  • If symptomatic (e.g., bleeding, petechiae)
  • If asymptomatic
    • Platelet levels < 50,000/mm3 → consider hematology referral to determine the underlying cause
    • Platelet levels > 50,000/mm3 → repeat CBC in 1–4 weeks
      • If decrease → hematology referral to determine the underlying cause
      • If increase → follow-up until normalization

References: [7]

Immune thrombocytopenic purpura (ITP)

Diagnosis of exclusion in isolated thrombocytopenia (< 150,000/mm3)

Splenomegaly is very unusual in ITP and makes other diagnoses more likely!

Suspect ITP in a child with thrombocytopenia and petechiae following a viral illness!