Situation: A nurse works in the pediatric rehabilitation clinic and the emergency room of a regional hospital. A 4-year-old with newly diagnosed acute lymphoblastic (lymphocytic) leukemia and a very high white cell count started induction chemotherapy, including asparaginase, 24 hours ago. The nurse reviews: Potassium: 6.3 mmol/L Phosphate: high Calcium: 7.0 mg/dL (1.75 mmol/L) Uric acid: high Urine output: falling over the last 6 hours Which complication do these findings MOST suggest?

Rapid breakdown of leukemic cells at the start of therapy releases potassium, phosphate, and uric acid; phosphate binds calcium, causing secondary hypocalcemia, and the crystals injure the kidneys. This pattern with falling urine output is tumor lysis syndrome, most common in leukemia with a high white cell count. Pancreatitis can lower calcium but does not raise potassium, phosphate, and uric acid together.

Clinical picture A 4-year-old with newly diagnosed acute lymphoblastic leukemia (ALL), a very high white cell count, and induction chemotherapy started 24 hours ago now shows a pattern of hyperkalemia, hyperphosphatemia, hypocalcemia, hyperuricemia, and falling urine output. This combination points to a metabolic emergency rather than an isolated organ problem.

Why the findings fit tumor lysis syndrome Rapid breakdown of leukemic blasts releases intracellular potassium, phosphate, and nucleic acids into the circulation. Nucleic acids are metabolized to uric acid, so serum uric acid rises. The released phosphate binds calcium, which lowers ionized and total calcium. Hyperkalemia, hyperphosphatemia, hyperuricemia, and secondary hypocalcemia occurring together after chemotherapy is the classic biochemical signature of tumor lysis syndrome (TLS). Uric acid and calcium phosphate crystals can then deposit in renal tubules, causing acute kidney injury and reduced urine output. TLS is defined by the presence of two or more of these metabolic abnormalities, and this child has all four plus declining renal function ^[1][4].

Why the other options do not explain the full picture Leukostasis from a high white cell count can cause respiratory or neurologic symptoms from sludging of blasts in small vessels, but it does not produce the combined electrolyte and uric acid pattern seen here. Acute pancreatitis from asparaginase can lower calcium through fat saponification, but it would not simultaneously raise potassium, phosphate, and uric acid. Dehydration from poor oral intake may reduce urine output, but it would not create hyperphosphatemia with hypocalcemia and hyperuricemia.

Finding	Mechanism in TLS	Clinical consequence
Hyperkalemia	Release of intracellular potassium from lysed blasts	Risk of arrhythmia, cardiac arrest
Hyperphosphatemia	Release of intracellular phosphate	Binds calcium, promotes crystal deposition
Hypocalcemia	Phosphate binding of calcium	Tetany, seizures, prolonged QT
Hyperuricemia	Nucleic acid breakdown to uric acid	Uric acid crystal nephropathy
Falling urine output	Renal tubular obstruction by crystals	Acute kidney injury, worsening electrolyte abnormalities

Pediatric ALL context ALL is one of the malignancies most strongly associated with TLS because of its high tumor burden and rapid cell turnover ^[4]. Children with a very high white cell count at diagnosis are at especially high risk, and TLS typically occurs early after induction chemotherapy begins . In a study of 91 children with ALL, TLS was a common complication characterized by the same biochemical abnormalities described in this scenario ^[1]. Another cohort of 5537 children with ALL identified TLS as a serious early complication, reinforcing the need for close monitoring in the first 24 to 72 hours of therapy .

Nursing priority The immediate nursing focus is prevention of life-threatening arrhythmias from hyperkalemia and protection of renal function through aggressive hydration and uric acid reduction. Watch out! Hypocalcemia in TLS is usually secondary to hyperphosphatemia; correcting calcium without first lowering phosphate can worsen calcium phosphate crystal deposition in tissues. Key point! Falling urine output in a child with ALL after starting chemotherapy is a red flag for TLS-related acute kidney injury, not simply dehydration, and requires urgent laboratory and renal monitoring ^[1][4].