What causes thrombocytopenia (low platelet count) during acute illness?

From the Guidelines

Thrombocytopenia during acute illness is primarily caused by increased platelet consumption, sequestration, or suppressed production, and management should focus on treating the underlying condition rather than the platelet drop itself. The pathophysiology of thrombocytopenia in acute illness involves several mechanisms, including increased clotting activity, splenic sequestration, and bone marrow suppression. Viral infections can directly suppress platelet production or trigger immune-mediated destruction, while bacterial infections may cause disseminated intravascular coagulation (DIC), consuming platelets 1.

Key Mechanisms and Management

• Increased platelet consumption due to clotting activity
• Splenic sequestration of platelets
• Suppressed platelet production in the bone marrow
• Management focuses on treating the underlying illness
• Monitoring platelet counts, with intervention necessary if counts fall below 10,000-20,000/μL or if there is significant bleeding

According to the AABB clinical practice guideline, prophylactic platelet transfusion is suggested for patients with a platelet count less than 20 × 10^9 cells/L undergoing elective central venous catheter placement, and less than 50 × 10^9 cells/L for elective diagnostic lumbar puncture, although the quality of evidence is low to very low 1. The threshold for prophylactic platelet transfusion in hospitalized patients with therapy-induced hypoproliferative thrombocytopenia is examined in several RCTs, suggesting that a threshold of 10 × 10^9 cells/L is associated with lower platelet usage and fewer transfusion reactions 1.

Prophylactic Platelet Transfusion Thresholds

• Less than 20 × 10^9 cells/L for central venous catheter placement
• Less than 50 × 10^9 cells/L for diagnostic lumbar puncture
• 10 × 10^9 cells/L threshold for prophylactic transfusion in therapy-induced hypoproliferative thrombocytopenia

In severe cases, platelet transfusions may be required, particularly if counts drop below 10,000/μL or if the patient is actively bleeding, as supported by the studies examining the effectiveness of prophylactic platelet transfusions in preventing bleeding complications 1. Most patients will see platelet recovery within days to weeks after the acute illness resolves, and if thrombocytopenia persists, further investigation for other causes should be pursued.

From the Research

Causes of Thrombocytopenia

• Thrombocytopenia can occur from decreased platelet production, increased destruction, splenic sequestration, or dilution or clumping 2
• In critically ill patients, thrombocytopenia may result from multiple mechanisms depending upon the underlying conditions and the current clinical setting 3
• Sepsis and trauma are the most common causes of thrombocytopenia in the ICU 4
• Thrombocytopenia can also be caused by heparin-induced thrombocytopenia, immune thrombocytopenia, and hepatic disease 2, 4

Mechanisms of Thrombocytopenia

• Consumption associated with thrombin-mediated platelet activation 5
• Platelet adhesion to endothelial cells and leucocytes 5
• Platelet aggregation by increased von Willebrand factor release 5
• Red cell damage and histone release 5
• Platelet destruction by the complement system 5
• Disseminated intravascular platelet activation may occur in case of systemic inflammatory syndromes, such as the response to sepsis 6

Clinical Significance of Thrombocytopenia

• Thrombocytopenia is associated with an increased incidence of bleeding complications 3
• A low platelet count is a strong and independent predictor of an adverse outcome in critically ill patients 6
• Persisting thrombocytopenia in critically ill patients is associated with, but not causative of, increased mortality 4
• Thrombocytopenia accounts as an independent determinant of poor outcomes in critically ill patients 3