What is Thrombocytopenia?
Thrombocytopenia is a condition defined as a platelet count below 150,000/μL (or 150 × 10⁹/L), which increases the risk of bleeding and can result from decreased platelet production, increased destruction, splenic sequestration, or dilution. 1, 2
Definition and Pathophysiology
- Thrombocytopenia represents a reduction in circulating platelets below the normal threshold of 150 × 10⁹/L 3, 1
- The condition arises through four main mechanisms: decreased bone marrow production, increased peripheral destruction, sequestration in an enlarged spleen, or hemodilution 1, 4
- It is important to note that thrombocytopenia itself is not a disease but rather a laboratory finding that reflects an underlying condition requiring identification 5
Clinical Severity Classification
The clinical manifestations correlate directly with the degree of platelet reduction:
- Mild thrombocytopenia (50-150 × 10⁹/L): Patients are typically asymptomatic and the condition is often discovered incidentally during routine blood work 6, 1
- Moderate thrombocytopenia (20-50 × 10⁹/L): Patients may develop cutaneous bleeding manifestations including easy bruising, petechiae (pinpoint red spots), and purpura (larger purple patches) 6, 1
- Severe thrombocytopenia (<20 × 10⁹/L): Significant risk of serious bleeding complications including gastrointestinal hemorrhage and life-threatening intracranial hemorrhage 6, 1
- Critical thrombocytopenia (<10 × 10⁹/L): Very high risk of spontaneous serious bleeding 1, 2
Important Clinical Caveat
Bleeding risk is not perfectly correlated with platelet count alone - additional factors significantly modify risk including patient age, lifestyle activities, comorbid conditions, and concurrent use of antiplatelet medications such as aspirin or NSAIDs 6
Common Etiologies
Thrombocytopenia occurs in diverse clinical contexts:
- Pregnancy-related: Affects 7-10% of pregnant women 2
- Immune-mediated disorders: Including immune thrombocytopenia (ITP), which is characterized by isolated thrombocytopenia without other obvious causes 7, 8
- Drug-induced: Particularly heparin-induced thrombocytopenia (HIT), which can occur in up to 1% of patients receiving unfractionated heparin 3, 2
- Cancer-related: Common complication affecting nearly all patients receiving certain chemotherapy regimens, particularly those with hematologic malignancies 3
- Infections: Various infectious processes can trigger thrombocytopenia 6, 4
- Liver disease and splenic sequestration 4, 5
- Hematologic emergencies: Including thrombotic microangiopathy (TMA) and disseminated intravascular coagulation (DIC) 2
Critical Paradox: Thrombosis Despite Low Platelets
A crucial pitfall is that certain thrombocytopenic conditions paradoxically increase thrombotic risk rather than just bleeding risk - these include heparin-induced thrombocytopenia, antiphospholipid syndrome, and thrombotic microangiopathies 3, 1. In cancer patients with thrombocytopenia, the risk of venous thromboembolism is not reduced despite low platelet counts, and prolonged thrombocytopenia (>30 days) is associated with a greater than four-fold increased risk of recurrent VTE 3
Activity Restrictions
Patients with platelet counts below 50 × 10⁹/L should avoid contact sports and activities that increase trauma risk to prevent bleeding complications 6, 1