What are the causes of thrombocytopenia?

Causes of Decreased Platelets (Thrombocytopenia)

Thrombocytopenia results from three primary mechanisms: decreased platelet production, increased platelet destruction, or splenic sequestration, with specific causes ranging from autoimmune disorders and infections to medications and bone marrow diseases.

Mechanistic Classification

Thrombocytopenia occurs through distinct pathophysiologic pathways 1, 2, 3:

Decreased Platelet Production

• Bone marrow infiltration: Leukemias, lymphomas, metastatic malignancies
• Bone marrow failure syndromes: Myelodysplastic syndromes, aplastic anemia, megaloblastic anemia
• Bone marrow fibrosis
• Nutritional deficiencies: Vitamin B12, folate deficiency

Increased Platelet Destruction

This is the most clinically significant category requiring urgent recognition:

Immune-mediated destruction:

• Primary immune thrombocytopenia (ITP): Autoimmune destruction of platelets, defined as platelet count <100 × 10⁹/L without other identifiable causes 4
• Secondary ITP associated with:
  • Autoimmune diseases: Systemic lupus erythematosus (SLE), antiphospholipid antibody syndrome 4, 5, 6
  • Viral infections: HIV, hepatitis C (HCV), which can be clinically indistinguishable from primary ITP 4, 5
  • Drug-induced: Prescription medications, quinine (tonic water), heparin 5, 3

Non-immune destruction:

• Disseminated intravascular coagulation (DIC): Activation of clotting cascade from sepsis or malignancy 7
• Thrombotic microangiopathies: Thrombotic thrombocytopenic purpura (TTP), hemolytic uremic syndrome (HUS) - these are medical emergencies 3, 7
• HELLP syndrome: Hemolysis, elevated liver enzymes, low platelets in pregnancy 3
• Heparin-induced thrombocytopenia (HIT): Requires immediate hospitalization 3

Splenic Sequestration

• Splenomegaly from any cause: Liver cirrhosis, portal hypertension, lymphoproliferative disorders 5
• Moderate to massive splenomegaly suggests alternative diagnosis to primary ITP 5

Dilutional Thrombocytopenia

• Massive transfusions
• Fluid resuscitation 2

Critical Diagnostic Considerations

Exclude Pseudothrombocytopenia First

Before pursuing extensive workup, collect blood in heparin or sodium citrate tube to exclude EDTA-dependent platelet clumping, which causes falsely low counts 5, 3. This laboratory artifact must always be ruled out initially.

Emergency Causes Requiring Immediate Hospitalization 3:

• Heparin-induced thrombocytopenia
• Thrombotic microangiopathies (TTP/HUS)
• HELLP syndrome
• Acute leukemia 7

Key Historical Red Flags 5:

Obtain detailed history for:

• Medications: All prescription, over-the-counter drugs, herbal supplements, quinine exposure
• Infections: HIV risk factors, hepatitis C, recent viral illnesses, vaccinations
• Autoimmune conditions: SLE, antiphospholipid syndrome
• Alcohol use: Chronic abuse causes multifactorial thrombocytopenia 7
• Liver disease: Cirrhosis causes sequestration and decreased production
• Family history: Inherited thrombocytopenias (Wiskott-Aldrich, Bernard-Soulier, MYH9-related disease) 5
• Recent transfusions: Posttransfusion purpura 5

Physical Examination Findings 5:

ITP typically shows:

• Isolated bleeding manifestations (petechiae, purpura, ecchymosis)
• Otherwise normal examination

Findings suggesting alternative diagnosis:

• Moderate/massive splenomegaly: Lymphoproliferative disorder, liver disease, not typical ITP
• Hepatomegaly or lymphadenopathy: Malignancy, HIV, SLE
• Fever, weight loss: Infection, malignancy
• Constitutional symptoms: Systemic disease

Laboratory Evaluation Algorithm

Initial Testing 5:

1. Complete blood count with peripheral smear review by qualified hematologist/pathologist - This is paramount

   • ITP shows isolated thrombocytopenia with otherwise normal CBC
   • Anemia should be proportional to bleeding only
   • Look for schistocytes (TTP/HUS), leukocyte inclusions (MYH9), giant/small platelets (inherited disorders)

2. HIV and HCV testing: Recommended for ALL adult patients regardless of risk factors or local prevalence 5

3. Blood group Rh(D) typing: If anti-D immunoglobulin therapy considered 5

Bone Marrow Examination 4, 5:

NOT routinely recommended for:

• Children/adolescents with typical ITP features (Grade 1B)
• Children failing IVIg therapy (Grade 1B)
• Before corticosteroids or splenectomy in typical cases (Grade 2C)

Consider in:

• Adults >60 years old 5
• Atypical features suggesting bone marrow pathology
• Abnormal CBC beyond isolated thrombocytopenia

Tests of Potential Utility 5:

• Antiphospholipid antibodies: If symptoms of antiphospholipid syndrome present
• Antinuclear antibodies: May predict chronicity in childhood ITP
• Thyroid function/antibodies: 8-14% of ITP patients develop thyroid disease
• Testing for acute infections: Parvovirus, CMV if clinically indicated

Tests NOT Routinely Recommended 5:

• Antiplatelet antibody assays (elevated in both immune and non-immune thrombocytopenia)
• Routine ANA testing in absence of SLE symptoms

Clinical Severity and Bleeding Risk 3:

• >50 × 10³/μL: Generally asymptomatic
• 20-50 × 10³/μL: Mild skin manifestations (petechiae, purpura, ecchymosis)
• <10 × 10³/μL: High risk of serious bleeding

Common Pitfalls to Avoid

1. Failing to exclude pseudothrombocytopenia - Always recheck with different anticoagulant
2. Missing drug-induced thrombocytopenia - Obtain comprehensive medication history including over-the-counter products
3. Overlooking HIV/HCV - Test all adults regardless of perceived risk
4. Assuming isolated thrombocytopenia is always ITP - Peripheral smear review is essential
5. Unnecessary bone marrow biopsies in typical pediatric ITP cases
6. Delaying recognition of emergencies - TTP, HIT, HELLP require immediate intervention
7. Ignoring moderate/massive splenomegaly - This suggests alternative diagnosis, not primary ITP