Management of Hyperleukocytosis

Initial Assessment and Intervention

The American College of Physicians recommends immediate initiation of aggressive intravenous hydration at 2.5-3 liters/m²/day and start hydroxyurea 50-60 mg/kg/day to achieve 50% WBC reduction within 1-2 weeks in patients with hyperleukocytosis (WBC >100,000/μL) 1
Aggressive IV hydration should be started immediately upon confirming hyperleukocytosis, titrating based on fluid balance, clinical status, and serial WBC monitoring 1
Hydroxyurea should be initiated concurrently with hydration once hyperleukocytosis is confirmed, without waiting for definitive diagnosis 1

A complete blood count with differential should be obtained to determine the specific pattern of WBC elevation and identify left shift (band neutrophils ≥6% or ≥1500 cells/mm³), which increases the likelihood ratio for bacterial infection from 3.7 to 14.5 2
Peripheral blood smear should be examined to assess band forms, blast cells, cell maturity, and toxic granulations 2
Bone marrow aspiration and biopsy should be performed immediately if acute leukemia is suspected based on peripheral smear findings 3

If infection is suspected, prompt empiric broad-spectrum antimicrobial therapy should be initiated based on the likely source of infection without waiting for culture results 2
If acute leukemia is confirmed, standard induction chemotherapy with cytarabine and an anthracycline (the "3+7" regimen) should be started once all diagnostic material has been obtained for non-promyelocytic AML 3
In patients with chronic myeloproliferative disorder, hydroxyurea should be used as the drug of choice to control proliferative myelomonocytic cells and reduce organomegaly 4

Platelets should be transfused if counts ≤10×10⁹/L to prevent bleeding complications 2
Prophylactic oral fluoroquinolones should be considered in patients with expected prolonged, profound granulocytopenia (<100/mm³ for two weeks) 2
Posaconazole should be used for antifungal prophylaxis in high-risk patients, as it significantly decreases fungal infections compared to fluconazole 2

Hydration and cytoreduction should not be delayed while waiting for definitive diagnosis in hyperleukocytosis 1
Leukapheresis should not be performed in APL without extreme caution due to hemorrhage risk 1
Treatment should not be delayed in suspected acute leukemia, as prompt institution of definitive therapy is essential after measures to rapidly reduce WBC count 2

The National Comprehensive Cancer Network recommends that growth factors should not be routinely used after induction chemotherapy, as they may confound bone marrow interpretation, and patients should be off GM-CSF or G-CSF for a minimum of 7 days before obtaining bone marrow to document remission 5
For patients with Acute Promyelocytic Leukemia (APL), the American Society of Hematology suggests initiating ATRA immediately once APL is suspected, and discontinuing if diagnosis is not confirmed genetically, with chemotherapy started without delay for WBC >10 × 10⁹/L, even if molecular results are pending 6
The National Comprehensive Cancer Network advises maintaining aggressive platelet transfusion support to keep platelets >50,000/μL and fibrinogen >150 mg/dL until coagulopathy resolves in APL patients 5, 6, 7
Monitoring for APL differentiation syndrome is crucial, and the National Comprehensive Cancer Network recommends initiating dexamethasone 10 mg BID for 3-5 days at first signs of fever, increasing WBC >10,000/μL, shortness of breath, hypoxemia, pleural/pericardial effusions 5, 6
The use of posaconazole for antifungal prophylaxis in high-risk patients is supported by the National Comprehensive Cancer Network, as it significantly decreases fungal infections compared to fluconazole 5