What is the difference between thrombocytosis and thrombocytopenia?

Thrombocytosis vs. Thrombocytopenia: Key Differences

Thrombocytosis and thrombocytopenia are opposite conditions - thrombocytosis is an abnormally high platelet count (>450 × 10⁹/L), while thrombocytopenia is an abnormally low platelet count (<150 × 10⁹/L).

Definition and Diagnostic Criteria

Thrombocytopenia

• Defined as platelet count <150 × 10⁹/L 1
• Clinical manifestations depend on severity:

  • 50 × 10⁹/L: Generally asymptomatic

  • 20-50 × 10⁹/L: Mild skin manifestations (petechiae, purpura, ecchymosis)
  • <10 × 10⁹/L: High risk of serious bleeding 1

Thrombocytosis

• Defined as platelet count >450 × 10⁹/L 2, 3
• Two main categories:
  • Primary thrombocytosis: Associated with hematological diseases (12.5% of cases) 3
  • Secondary/reactive thrombocytosis: Response to underlying conditions (87.7% of cases) 3, 4

Etiology

Thrombocytopenia Causes

• Decreased platelet production
• Increased platelet destruction
• Splenic sequestration
• Dilution or clumping 1
• Common specific causes:
  • Immune thrombocytopenic purpura (ITP)
  • Drug-induced thrombocytopenia
  • Heparin-induced thrombocytopenia (HIT)
  • Thrombotic microangiopathies
  • HELLP syndrome in pregnancy
  • Hepatic disease 2, 1

Thrombocytosis Causes

• Primary thrombocytosis (12.5%):
  • Essential thrombocythemia (most common)
  • Other myeloproliferative neoplasms
  • 86% have at least one molecular marker (e.g., JAK2V617F mutation) 3
• Secondary thrombocytosis (87.7%):
  • Tissue injury/damage (32-42%)
  • Infections (17-24%)
  • Chronic inflammatory disorders (10-12%)
  • Iron deficiency anemia (11%)
  • Malignancy (13%) 3, 4

Clinical Significance and Complications

Thrombocytopenia

• Primary concern: Bleeding risk
• Risk increases as platelet count decreases
• Some conditions (HIT, antiphospholipid syndrome) paradoxically increase thrombosis risk despite low platelets 1

Thrombocytosis

• Primary thrombocytosis:
  • Higher risk of both arterial and venous thromboembolic events
  • Higher median platelet counts 3, 4
• Secondary thrombocytosis:
  • Thromboembolic events mainly restricted to venous system
  • Occur only with additional risk factors
  • Generally lower thrombotic risk 4

Management Approaches

Thrombocytopenia Management

• Treat underlying cause when possible
• Platelet transfusion indicated for:
  • Active hemorrhage
  • Platelet counts <10 × 10⁹/L 2, 1
• Activity restrictions for patients with counts <50 × 10⁹/L 2
• Specific treatments for ITP:
  • First-line: Corticosteroids, IVIG, IV anti-D (if Rh-positive)
  • Second-line: Thrombopoietin receptor agonists, rituximab, splenectomy 2

Thrombocytosis Management

• Primary thrombocytosis:
  • May require cytoreductive therapy
  • Aspirin therapy effective for reducing thrombotic risk 5
• Secondary thrombocytosis:
  • Focus on treating underlying cause
  • Antithrombotic therapy generally not indicated unless additional risk factors present 2

Laboratory Differentiation

• Primary vs. secondary thrombocytosis can be distinguished by:
  • Higher platelet counts in primary thrombocytosis
  • Differences in leukocyte count, hematocrit, ESR, fibrinogen, potassium, and LDH levels 4
• Reticulated platelet percentage (RP%) and absolute count:
  • Significantly higher in thrombocytosis patients with thrombotic complications
  • May help assess thrombotic risk and treatment response 5

Procedural Considerations

• Thrombocytopenia requires specific platelet count thresholds for procedures:
  • Central venous catheter insertion: >20 × 10⁹/L
  • Lumbar puncture: >40 × 10⁹/L
  • Major surgery: >50 × 10⁹/L
  • Epidural procedures: >80 × 10⁹/L
  • Neurosurgery: >100 × 10⁹/L 2

Anticoagulation Considerations

• In thrombocytopenia:
  • Full therapeutic anticoagulation safe with counts >50 × 10⁹/L
  • Dose adjustments or holding anticoagulants with lower counts 2
• In thrombocytosis:
  • Primary thrombocytosis may require antiplatelet therapy
  • Secondary thrombocytosis generally doesn't require antiplatelet therapy unless additional risk factors present 2