Thrombocytopenia

Overview of Thrombocytopenia

Definition: A condition characterized by a decreased platelet count in the peripheral blood. Generally defined as a platelet count less than 150 x 10^9/L (150,000/µL).
Significance: Thrombocytopenia increases the risk of bleeding, with the severity of bleeding correlating with the degree of platelet reduction.
Classification:
- Based on Mechanism:
  - Increased Platelet Destruction (Immune and Non-Immune)
  - Decreased Platelet Production
  - Sequestration (less common)
  - Dilutional
  - Pseudothrombocytopenia (Spurious Thrombocytopenia)
- Based on Severity:
  - Mild Thrombocytopenia: 100-150 x 10^9/L
  - Moderate Thrombocytopenia: 50-99 x 10^9/L
  - Severe Thrombocytopenia: <50 x 10^9/L

Immune Thrombocytopenic Purpura (ITP):
- Definition: An acquired autoimmune disorder characterized by the destruction of platelets by autoantibodies
Thrombotic Thrombocytopenic Purpura (TTP):
- Definition: A life-threatening disorder characterized by thrombotic microangiopathy (TMA), leading to microvascular thrombosis, thrombocytopenia, and hemolytic anemia
Heparin-Induced Thrombocytopenia (HIT):
- Definition: A prothrombotic disorder caused by antibodies against heparin-platelet factor 4 (PF4) complexes

Definition: A falsely low platelet count due to in vitro platelet clumping or satellitism

Complete Blood Count (CBC) with Peripheral Blood Smear: Essential for diagnosing and classifying thrombocytopenia
Reticulocyte Count: Assesses bone marrow response
Coagulation Studies (PT, aPTT, Fibrinogen, D-dimer): To evaluate for DIC
Direct Antiglobulin Test (DAT): To evaluate for autoimmune hemolytic anemia (Evans syndrome)
HIV Testing: To rule out HIV-associated thrombocytopenia
Hepatitis C Testing: To rule out hepatitis C-associated thrombocytopenia
Bone Marrow Aspiration and Biopsy: May be necessary to evaluate for bone marrow disorders (e.g., aplastic anemia, MDS)
ADAMTS13 Activity Assay: To diagnose TTP
HIT Antibody Testing: To diagnose heparin-induced thrombocytopenia

Thrombocytopenia: Decreased platelet count
Purpura: Bruising due to bleeding under the skin
Petechiae: Small, pinpoint hemorrhages
Idiopathic Thrombocytopenic Purpura (ITP): Autoimmune destruction of platelets
Thrombotic Thrombocytopenic Purpura (TTP): Thrombotic microangiopathy due to ADAMTS13 deficiency
Heparin-Induced Thrombocytopenia (HIT): Thrombocytopenia caused by antibodies against heparin-PF4 complexes
Schistocytes: Fragmented red blood cells (seen in TTP and other microangiopathic hemolytic anemias)
Pseudothrombocytopenia: Falsely low platelet count due to in vitro platelet clumping or satellitism
Megakaryocytes: Bone marrow cells that produce platelets