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Thrombocytopenia USMLE Notes & Mnemonics contains all the high-yield points you need to know.


  • Thrombocytopenia: A condition characterized by abnormally low levels of platelets (thrombocytes) in the blood, typically less than 150,000 platelets per microliter. (Ref)


  • Can be categorized based on mechanism:
    • Decreased Production: Bone marrow disorders, chemotherapy, alcohol, viral infections (HIV, HCV), vitamin B12 or folate deficiency.
    • Increased Destruction: Immune (ITP, drugs, post-transfusion), Non-immune (TTP, HUS, DIC, mechanical destruction by artificial heart valves).
    • Sequestration: Hypersplenism.
    • Dilutional: Massive transfusions.

Clinical Features:

  • Bleeding: Petechiae, purpura, mucosal bleeding, prolonged bleeding after procedures.
  • Asymptomatic: Often found incidentally on CBC.


  • Complete Blood Count (CBC): Confirms low platelet count.
  • Peripheral Blood Smear: To evaluate platelet morphology, schistocytes in TTP/HUS, large platelets in ITP.
  • Bone Marrow Biopsy: If bone marrow pathology is suspected.
  • Coagulation Studies: To rule out coagulopathies like DIC.


  • Based on cause; general measures include:
    • Platelet Transfusion: For significant bleeding or extremely low counts (<10,000/microliter).
    • Treat Underlying Cause: Antibiotics for infections, stop offending drugs, etc.
    • Immunosuppressive Therapy: For ITP (e.g., corticosteroids, IVIG, rituximab).
    • Plasma Exchange: For TTP.

High-Yield Mnemonic: “PLATELETS” for Causes of Thrombocytopenia

  • Production decreased
  • Liver disease
  • Alcohol
  • Enlarged spleen (Hypersplenism)
  • Lupus and other autoimmune disorders
  • Endotoxemia (DIC)
  • Transfusion (post-transfusion purpura)
  • Sepsis
‎Thrombocytopenia causes mnemonic
‎Thrombocytopenia causes mnemonic

Chart: Diagnostic Approach to Thrombocytopenia

Platelet Count<150,000/microliterDiagnosis of thrombocytopenia
Peripheral Blood SmearPlatelet morphology, schistocytesHelps identify cause
Coagulation Studies (PT, aPTT)Normal in isolated thrombocytopenia; abnormal in DICDifferentiate from coagulopathies
Bone Marrow BiopsyCellularity, MegakaryocytesAssess for production issue
LDH, Bilirubin, HaptoglobinElevated LDH, Low HaptoglobinSuggestive of hemolysis (TTP/HUS)
Antiphospholipid AntibodiesPositiveSuggestive of immune-mediated

High-Yield Facts:

  • ITP in Children: Often follows a viral infection and is usually self-limited.
  • ITP in Adults: More often chronic, women > men, associated with other autoimmune conditions.
  • TTP: ADAMTS13 deficiency leads to large vWF multimers, causing platelet aggregation and microangiopathic hemolytic anemia.
  • HUS: Typically follows diarrheal illness (E.coli O157:H7), presents with renal failure.
  • DIC: Associated with sepsis, malignancy, obstetric complications; characterized by widespread microvascular thrombosis and bleeding.

Check other important USMLE Notes

Note: In clinical vignettes, look for clues to the underlying cause of thrombocytopenia for proper management. The presence of anemia, renal failure, or neurological symptoms may suggest a microangiopathic process such as TTP or HUS. Always consider medication history, recent transfusions, and evidence of infections as potential etiologies.

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