The selective removal of platelets from the circulation to reduce dangerously elevated platelet counts in patients with myeloproliferative neoplasms. Used as an emergency temporizing measure when thrombocytosis poses an immediate risk of thrombotic or hemorrhagic complications.
Therapeutic thrombocytapheresis uses centrifugal apheresis to selectively collect and remove platelets from the patient's blood. The instrument separates blood components by density, collecting the platelet-rich fraction while returning red blood cells, plasma, and other components to the patient.
Extreme thrombocytosis — typically defined as a platelet count exceeding 1,000,000/µL (1,000 × 10⁹/L) — occurs in myeloproliferative neoplasms including essential thrombocythemia (ET), polycythemia vera (PV), and chronic myelogenous leukemia (CML). At very high counts, the excess platelets paradoxically increase bleeding risk (acquired von Willebrand syndrome) while simultaneously increasing thrombotic risk through platelet aggregation and microvascular occlusion.
A single session of thrombocytapheresis can reduce the platelet count by 30–50%. However, the bone marrow rapidly produces new platelets, causing counts to rebound within days. Thrombocytapheresis is therefore a temporizing emergency measure, used to rapidly reduce platelet counts while cytoreductive pharmacological therapy (hydroxyurea, anagrelide) takes effect.
Rebound Effect: Platelet counts rebound rapidly after thrombocytapheresis because the underlying bone marrow overproduction is not addressed. Cytoreductive therapy (hydroxyurea, anagrelide, interferon) must be initiated concurrently to achieve sustained platelet count reduction.
Acquired von Willebrand Syndrome: At very high platelet counts (>1,500,000/µL), large von Willebrand factor multimers are adsorbed onto the excess platelet surface, reducing circulating vWF activity and causing a bleeding diathesis similar to type 2A vWD. Paradoxically, aspirin and antiplatelet therapy may worsen bleeding in this setting.
Pregnancy Indication: Thrombocytapheresis may be used in pregnant patients with extreme thrombocytosis when cytoreductive agents are contraindicated due to teratogenicity. Hydroxyurea is teratogenic; anagrelide crosses the placenta. Thrombocytapheresis provides a drug-free option for platelet count reduction during pregnancy.
| Condition | Category | Grade | Notes |
|---|---|---|---|
| Thrombocytosis — Symptomatic | II | 2C | Emergency cytoreduction; bridge to cytoreductive therapy |
| Thrombocytosis — Pregnancy | II | 2C | When cytoreductive agents are contraindicated; drug-free option |
| Thrombocytosis — Prophylactic | III | 2C | Asymptomatic extreme thrombocytosis; evidence limited |