19.2 Hyperleukocytosis

CPHON TCO V.D.3 is hyperleukocytosis: a very high white-cell count (WBC) that can sludge in the microcirculation. This is not polycythemia, not the tumor-lysis laboratory chapter (though lysis starts when you treat), and not a demand that you memorize a single ONCC-published WBC cutoff. Many bedside pathways flag counts well above 100,000/µL, and acute myeloid leukemia (AML)—especially monoblastic disease—can produce leukostasis at lower counts than acute lymphoblastic leukemia (ALL) because myeloid blasts are large and sticky. T-cell ALL (T-ALL) is the other classic high-count picture.

A 6-year-old with monoblastic AML, a WBC of 180,000/µL, and new confusion, and a 15-year-old with T-ALL, a mediastinal mass, and a WBC of 250,000/µL are the CPHON emergencies.

Who sludges and what you see

Leukostasis is blast packing in pulmonary and cerebral capillaries. The child does not look like volume overload from a transfusion; the child looks like respiratory distress, visual change, and confusion (or headache, ataxia, or a new focal finding). Pulse oximetry may fall. The chest radiograph may show interstitial infiltrates that mimic pneumonia or pulmonary hemorrhage. Fundoscopic examination looks for retinal hemorrhages, cotton-wool spots, and papilledema—the eyes are a window on the same microcirculation that is failing in the brain. Do not skip the fundoscopic exam because the child is just anxious about the diagnosis.

Monoblastic and myelomonocytic AML (historically FAB M4/M5) also infiltrate gums and skin; gingival hypertrophy plus a sky-high WBC is a viscosity story, not a dental appointment. T-ALL adds a mediastinal mass airway risk—signpost the cardiopulmonary-emergency chapter for the mass itself, but the high count still needs this page.

Walk the 6-year-old. Newly diagnosed monoblastic AML. WBC 180,000/µL, hemoglobin 6.2 g/dL, platelets 12,000/µL. The child is tachypneic, says the lights have halos, and does not know the parent's name. This is leukostasis. Oxygen, intensive-care unit (ICU) transfer, and a fundoscopic exam happen now, while the team chooses cytoreduction. It is not a floor observation for the first night of teaching videos.

Distinguish polycythemia

Polycythemia is too much red-cell mass—high hematocrit, high hemoglobin—not too many leukocytes. Viscosity is high because erythrocytes are the main determinant of blood viscosity. Pediatric polycythemia (cyanotic heart disease, high-altitude physiology, rare myeloproliferative disease) is a different map: phlebotomy or red-cell reduction, not hydroxyurea for blasts. Do not treat a high WBC with a hematocrit protocol, and do not treat a hematocrit of 68% as hyperleukocytosis. The CPHON trap is transfusing packed red blood cells (PRBC) into a hyperleukocytosis child as if the only number that mattered were the hemoglobin.

First actions: water, oxygen, careful blood, cytoreduction

Hydration lowers viscosity by diluting the circulating blast burden and protects tubules for the tumor lysis syndrome (TLS) that starts when therapy begins. Initial fluids typically contain no potassium, as in the TLS chapter. Watch the lungs: a child with leukostasis already has a pulmonary capillary problem; dump-in volume without reassessment is how you add pulmonary edema to sludge.

Avoid routine PRBC until the WBC is reduced. Raising hematocrit raises viscosity and can worsen leukostasis and intracranial catastrophe. Anemia is real—the 6.2 g/dL still matters—but the first hours are oxygen, cytoreduction, and a team decision about a small, slow red-cell aliquot if ischemia is extreme, not a reflex two-unit catch-up. Platelets may still be given for bleed risk. Thrombocytopenia plus hyperleukocytosis is an intracranial-hemorrhage setup; platelet transfusion does not raise viscosity the way red cells do. Give platelets as ordered for a wet mouth, headache, or a critically low count.

Cytoreduction is a team choice, not a nurse-invented recipe:

• Hydroxyurea to lower the count while induction is organized
• Leukapheresis for selected children with symptomatic leukostasis and a usable access plan—calcium, circuit, and blood-volume issues are real in small children. Leukapheresis does not replace disease-directed therapy
• Induction chemotherapy is the definitive blast-clearing move

Oxygen and ICU monitoring belong with symptomatic leukostasis. Telemetry, frequent neurologic checks, and a working airway plan sit next to the fundoscope. Do not send a confused, hypoxic newly diagnosed AML patient to a regular floor.

TLS when therapy starts

The metabolic-emergencies chapter owns the laboratory four. This page owns the reminder: the count does not vanish quietly. Hydroxyurea, leukapheresis, steroids in T-ALL, and induction all dump potassium, phosphate, and uric acid. Start TLS precautions with cytoreduction—hydration without potassium, allopurinol or rasburicase per protocol, telemetry—not after the first arrhythmia. A 15-year-old with T-ALL whose WBC is crashing after the first steroid doses is a TLS patient even if leukostasis is improving.

Teach families why the red-cell bag is being held, why platelets may still go in, why the eye doctor is in the room, and why the child is in the ICU: the white cells are crowding the smallest blood vessels in the lungs, brain, and retina. That sentence is more useful than the word hyperleukocytosis alone.

That is TCO V.D.3: name monoblastic AML and T-ALL, treat respiratory-visual-confusion clusters as leukostasis, hydrate, hold routine PRBC, give platelets when bleeding is the risk, start hydroxyurea or leukapheresis or induction as the team orders, watch TLS, and look in the eyes.