Thrombocytopenia USMLE Notes & Mnemonics contains all the high-yield points you need to know.
Definition:
- Thrombocytopenia: A condition characterized by abnormally low levels of platelets (thrombocytes) in the blood, typically less than 150,000 platelets per microliter. (Ref)
Etiology:
- 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.
Diagnosis:
- 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.
Management:
- 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
- TTP/HUS
- Enlarged spleen (Hypersplenism)
- Lupus and other autoimmune disorders
- Endotoxemia (DIC)
- Transfusion (post-transfusion purpura)
- Sepsis
Chart: Diagnostic Approach to Thrombocytopenia
| Test/Feature | Finding | Implication |
|---|---|---|
| Platelet Count | <150,000/microliter | Diagnosis of thrombocytopenia |
| Peripheral Blood Smear | Platelet morphology, schistocytes | Helps identify cause |
| Coagulation Studies (PT, aPTT) | Normal in isolated thrombocytopenia; abnormal in DIC | Differentiate from coagulopathies |
| Bone Marrow Biopsy | Cellularity, Megakaryocytes | Assess for production issue |
| LDH, Bilirubin, Haptoglobin | Elevated LDH, Low Haptoglobin | Suggestive of hemolysis (TTP/HUS) |
| Antiphospholipid Antibodies | Positive | Suggestive 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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