What is the cause of leukocytosis (elevated white blood cell count) and thrombocytosis (elevated platelet count) following splenectomy (removal of the spleen)?

From the Guidelines

Leukocytosis and thrombocytosis occur after splenectomy due to the loss of the spleen's filtering mechanism, which normally removes aging blood cells from circulation. This is because the spleen typically sequesters approximately 30% of platelets and a significant portion of white blood cells, particularly lymphocytes 1. When the spleen is removed, this sequestration is lost, leading to increased numbers of white blood cells and platelets in the bloodstream.

Key Points to Consider

• The spleen plays a crucial role in removing abnormal or damaged blood cells, so its absence allows these cells to persist longer in circulation.
• The post-splenectomy effect is most pronounced in the first few weeks to months after surgery but may persist long-term.
• Patients should be monitored with complete blood counts, and clinicians should be aware that these elevated counts represent a new baseline rather than a pathological process requiring intervention, as suggested by the American Society of Hematology 1.
• However, extremely high platelet counts may warrant consideration of prophylactic antiplatelet therapy to prevent thrombotic complications.

Clinical Implications

• Clinicians should be cautious not to misinterpret elevated white blood cell and platelet counts as a sign of infection or other pathology in post-splenectomy patients.
• Instead, these counts should be considered in the context of the patient's overall clinical picture and the expected effects of splenectomy on blood cell counts 1.
• The management of patients after splenectomy should focus on monitoring for potential complications, such as thrombotic events, rather than attempting to normalize blood cell counts.

From the Research

Leukocytosis and Thrombocytosis after Splenectomy

• Leukocytosis and thrombocytosis are common findings after splenectomy, as reported in several studies 2, 3, 4, 5, 6.
• The exact mechanisms behind these changes are not fully understood, but they are thought to be related to the removal of the spleen's filtering function and the subsequent increase in circulating blood cells.
• Studies have shown that patients who undergo splenectomy have higher white blood cell (WBC) counts and platelet counts compared to those who do not undergo splenectomy 2, 4, 6.
• The increase in WBC count is thought to be due to the removal of the spleen's role in filtering out old or damaged white blood cells, leading to an increase in circulating WBCs 2.
• The increase in platelet count is thought to be due to the removal of the spleen's role in sequestering platelets, leading to an increase in circulating platelets 3, 5.

Comparison of Elective and Emergency Splenectomy

• Studies have compared the hematologic changes after elective and emergency splenectomy, with some finding that emergency splenectomy leads to more profound and persistent hematologic changes 4.
• However, other studies have found that the type of splenectomy (elective or emergency) does not significantly affect the incidence of thrombocytosis or leukocytosis 5, 6.

Association with Thromboembolic Events and Infection

• Some studies have investigated the association between thrombocytosis and leukocytosis after splenectomy and the risk of thromboembolic events or infection 4, 5.
• While there is some evidence to suggest that thrombocytosis and leukocytosis may be associated with an increased risk of thromboembolic events or infection, the relationship is not fully understood and requires further study 4, 5.