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In some leukaemias the white cell count is so high that the blood thickens and blocks small vessels in the lungs, brain and kidneys. This leukostasis is an emergency. The cells are brought down quickly with hydroxyurea and then chemotherapy; sometimes a machine filters them out. Blood transfusions are avoided unless really needed, because they thicken the blood further.
Hyperleukocytosis is a white cell count above 100,000/µL from leukaemic proliferation; leukostasis is end-organ injury from it, which can occur at lower counts and is commoner in AML than ALL because myeloid blasts are larger (ATS Scholar 2025). The lungs, kidneys and brain are most affected; intracranial haemorrhage is the most feared complication. Tumour lysis syndrome (up to 10%) and DIC (30 to 40%) accompany it. Diagnosis is usually presumptive. There should be a low threshold for intensive care.
Supportive care: fluids with close fluid-balance monitoring, electrolytes and uric acid at least every 6 hours, allopurinol or rasburicase, red cell transfusion only for symptomatic anaemia because it raises viscosity, and prompt platelets, plasma and fibrinogen for DIC. Cytoreduction: hydroxyurea before induction chemotherapy; all-trans retinoic acid at once if acute promyelocytic leukaemia is suspected. Leukapheresis can be considered but is institution-specific; a 2026 meta-analysis of 13 retrospective studies (1406 patients in the main analysis) found no clear reduction in 30-day mortality (OR 0.94, 95% CI 0.65 to 1.34; very low certainty). Red cell exchange is reported as an alternative for rapid leukoreduction (Blood 2024). ASFA's tenth edition (2026) categorises leukocytapheresis, but its category could not be read.
Why: People can deteriorate quickly, with breathing failure or bleeding in the brain.
“These patients may experience rapid decompensation, and there should be a low threshold to admit them to an intensive care unit (Figure 1).”
Why: Organ damage can happen at lower counts, and the diagnosis is usually made on clinical grounds.
“Leukostasis is a clinical emergency characterized by end-organ injury from malignant hyperleukocytosis but can also occur at WBC counts <100,000/μl (2).”
Why: Fluids dilute the blood and protect the kidneys, but too much can worsen breathing.
“Although vigorous fluid administration can reduce WBC concentration and blood viscosity and mitigate consequences of TLS, it has a potential to cause volume overload and exacerbate respiratory impairment, so close monitoring of fluid balance is important.”
Why: Leukaemia cells breaking down release potassium, phosphate and uric acid that can damage the kidneys and heart.
“Given the high risk of TLS, frequent electrolyte and uric acid monitoring (at least every 6 h) is needed.”
Why: Adding red cells makes thick blood thicker and can worsen the blockage.
“Blood transfusions should be avoided unless the patient has symptomatic anemia because increased blood viscosity can worsen leukostasis.”
Why: Clotting failure is common and, with leukostasis, raises the risk of bleeding in the brain.
“DIC is common, and treatment with platelets, fresh frozen plasma, and fibrinogen should be promptly initiated if this is suspected.”
Why: Bringing the count down quickly relieves the blockage; promyelocytic leukaemia needs its own urgent treatment.
“If acute promyelocytic leukemia is suspected, all-trans retinoic acid should be initiated immediately to induce differentiation (1).”
Why: Filtering the white cells out works quickly, but it has not been shown to save lives and practice differs between hospitals.
“Additionally, the beneficial effect on early clinical outcomes with leukapheresis has not been definitively demonstrated (2).”
How care is usually carried out, read from the guidelines and standards cited. Your own team's protocol and their judgement come first; this page is for understanding it, not for doing it yourself.
No graded guideline on hyperleukocytosis could be read for this page. The sources read agree on supportive care (fluids with care, tumour lysis prophylaxis, avoiding unnecessary red cell transfusion, correcting DIC) and on rapid cytoreduction with hydroxyurea and then induction chemotherapy, with ATRA at once for suspected promyelocytic leukaemia. They disagree, or are uncertain, about leukapheresis: the ATS Scholar article and the Journal of Hospital Medicine review describe it as optional and institution-dependent, and the 2026 meta-analysis of 13 retrospective studies found no clear effect on 30-day mortality, at very low certainty. ASFA (2026) gives the formal apheresis category but could not be read.
ATS Scholar (American Thoracic Society) 2025 · Journal of Hospital Medicine 2026 · Expert Review of Hematology 2026 · American Society for Apheresis, Journal of Clinical Apheresis 2026
Where it differs: Removes leukaemic cells by apheresis as soon as the count is very high or leukostasis is suspected, alongside cytoreduction.
Evidence: 2026 meta-analysis: 13 retrospective comparative studies; 30-day mortality OR 0.94 (95% CI 0.65 to 1.34), most studies at serious risk of bias, certainty very low, with confounding by indication.
Where it differs: Uses red cell exchange to remove white cells, which can also correct severe anaemia without raising viscosity.
Evidence: Blood 2024: similar leukoreduction to standard therapeutic leukoreduction, possibly better in severe anaemia, monocytic leukaemias or when rapid treatment is needed. Read as an abstract only.
Where it differs: Uses cytarabine as well as hydroxyurea to bring the count down until definitive treatment starts.
Evidence: Named in the Journal of Hospital Medicine 2026 review abstract; no comparative data read.
| Recommendation | Grade, as printed | Source |
|---|---|---|
| Leukapheresis and 30-day mortality in AML with hyperleukocytosis “Most studies were at serious risk of bias, and certainty of evidence was very low.” | GRADE: very low certainty | Expert Review of Hematology 2026 |
Shares Cytarabine, Acute lymphoblastic leukaemia, Acute myeloid leukaemia and the tags protocol, acute-oncology, oncological-emergency.
Shares Allopurinol, Rasburicase, Tumour lysis syndrome (TLS), Acute lymphoblastic leukaemia.
Shares the tags protocol, acute-oncology, oncological-emergency.
Shares the tags protocol, acute-oncology, oncological-emergency.
Shares the tags protocol, acute-oncology, oncological-emergency.
Shares the tags protocol, acute-oncology, oncological-emergency.
Shares the tags protocol, acute-oncology, oncological-emergency.
Shares the tags protocol, acute-oncology, oncological-emergency.