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compounded by coagulopathy from the leukemia itself or from disseminated
intravascular coagulation (DIC) related to sepsis.
Tumor Lysis Syndrome. Tumor proliferation or chemotherapy can lead to rapid
tumor lysis, in which the release of intracellular contents increases serum levels of
lactate dehydrogenase (LDH), potassium, phosphate, and uric acid with potentially
severe metabolic consequences. Tumor lysis is common with acute leukemias and
lymphomas but can also occur with neuroblastoma or other solid tumors with a very
high tumor burden.
Calcium complexes with phosphate to form calcium phosphate crystals that can
deposit in the renal tubules and other tissue sites. This can result in renal
insufficiency and hypocalcemia. Urate crystals can precipitate in the acidic urine
encountered in the renal tubules causing an obstructive uropathy and renal
insufficiency. Tumor lysi s syndrome (TLS) occurs when these electrolyte
derangements occur with evidence of renal insufficiency or failure.
Fortunately, effective preventive strategies make clinically significant TLS a rare
occurrence. Screening and preemptive therapy with hydration and allopurinol is
appropriate for all patients at risk for TLS. The use of allopurinol or rasburicase to
decrease uric acid levels is often driven by institutional protocol. A full discussion
of the management of tumor lysis is found in Section II.
Hyperleukocytosis. Hyperleukocytosis is defined as WBC count above
100,000/mm3. When hyperleukocytosis is present, the clinical findings of
leukostasis may develop from sludging of WBCs in the capillary beds. The most
vulnerable beds are those in the lungs and CNS where increased viscosity can cause
either thrombosis or hemorrhage. Leukostasis is much more common with myeloid
leukemia than with ALL. In the setting of hyperleukocytosis, hydration should be
initiated immediately to reduce viscosity. Transfusion of red blood cells and
diuretics should be avoided to prevent further increases in blood viscosity, but
platelet transfusion is appropriate to reduce the risk of CNS hemorrhage.
Leukocytopheresis, a technique to reduce blood viscosity acutely, should be initiated
immediately in the presence of respiratory or neurologic symptoms, even if mild.
The use of prophylactic leukocytopheresis is controversial and should be considered

only in consultation with a pediatric oncologist. Since new-onset leukemia may be
associated with coagulopathy, we recommend obtaining coagulation studies to
determine the risk of bleeding during leukocytopheresis.
Extramedullary Involvement. As leukemia develops, malignant cells may infiltrate
nonhematopoietic tissues, producing adenopathy, hepatomegaly, and splenomegaly.
Anterior mediastinal masses (AMM) occur primarily with T-lineage ALL and can