# A nurse is caring for a patient with acute leukemia who develops tumor lysis syndrome. Which laboratory finding requires the most immediate intervention?

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## 문제

A nurse is caring for a patient with acute leukemia who develops tumor lysis syndrome. Which laboratory finding requires the most immediate intervention?

## 보기

1. Serum uric acid level of 12 mg/dL (normal: 3.5-7.2 mg/dL)
2. Serum phosphorus level of 8.5 mg/dL (normal: 3.0-4.5 mg/dL)
3. Serum potassium level of 5.8 mEq/L (normal: 3.5-5.0 mEq/L)
4. Serum calcium level of 6.2 mg/dL (normal: 9.0-10.5 mg/dL) **✔ 정답**

**정답: 4**

## 해설

Severe hypocalcemia (calcium 6.2 mg/dL) in tumor lysis syndrome requires immediate intervention due to risk of life-threatening tetany, laryngospasm, and cardiac arrhythmias. Other electrolyte imbalances (hyperuricemia, hyperphosphatemia, hyperkalemia) also need management but are less immediately life-threatening.

## 심화 해설

Clinical Reasoning and Prioritization

The correct answer is the finding that requires the most immediate intervention: the serum calcium level of 6.2 mg/dL. In the context of Tumor Lysis Syndrome (TLS), all four laboratory values are critically abnormal and represent the classic metabolic quartet of this oncologic emergency: hyperuricemia, hyperkalemia, hyperphosphatemia, and hypocalcemia [1]. The key to answering this NCLEX-RN priority question lies in understanding which derangement poses the most immediate, life-threatening risk of sudden cardiac arrest.

Pathophysiology of the Immediate Threat

The severe hypocalcemia in TLS is a direct consequence of the rapid cell destruction releasing massive amounts of intracellular phosphate into the bloodstream. This leads to hyperphosphatemia, as evidenced by the level of 8.5 mg/dL. The excess serum phosphorus then binds to calcium, forming insoluble calcium-phosphate crystals that deposit in tissues, thereby precipitously lowering the ionized (active) serum calcium [1]. While hyperkalemia is famously cardiotoxic, the profound hypocalcemia in this scenario is the most urgent finding because it directly destabilizes myocardial cell membranes. Severe hypocalcemia causes prolonged QT intervals, which can rapidly degenerate into Torsades de Pointes and fatal ventricular arrhythmias . This neurological and cardiac dysfunction from severe hypocalcemia demands immediate correction to prevent cardiac arrest .

Analysis of Other Critical Findings

While all findings require intervention, they are ranked here by the acuity of their life-threatening potential in the context of the question's specific values.

- Serum potassium of 5.8 mEq/L (Option 3): This represents moderate hyperkalemia, a hallmark of TLS that requires urgent treatment due to the risk of life-threatening cardiac arrhythmias [1,4]. However, a level of 5.8 mEq/L, while dangerous, typically produces peaked T-waves on ECG and does not carry the same instantaneous risk of sudden cardiac standstill as the profound hypocalcemia presented here. Management includes cardiac monitoring and shifting potassium intracellularly, but the hypocalcemia-induced membrane instability is the more immediate trigger for lethal arrhythmias .

- Serum phosphorus of 8.5 mg/dL (Option 2): This level is critically high and is the direct cause of the hypocalcemia. The immediate danger of hyperphosphatemia itself is not direct cardiac arrhythmia, but rather the resulting hypocalcemia and potential for acute kidney injury from calcium-phosphate crystal deposition. The treatment priority is to address the hypocalcemia it has caused [1].

- Serum uric acid of 12 mg/dL (Option 1): This severe hyperuricemia is a key feature of TLS and can lead to uric acid nephropathy and acute kidney injury. While this requires prompt intervention with aggressive hydration and rasburicase or allopurinol, the threat is subacute renal failure, not immediate cardiac arrest within minutes [1].

NCLEX-RN Priority-Setting Framework

This question tests the application of the "ABC" (Airway, Breathing, Circulation) priority-setting framework. A life-threatening electrolyte disturbance that directly impairs cardiac conduction and contractility is a "Circulation" emergency of the highest order. Severe hypocalcemia causes neuromuscular and cardiac membrane instability that can lead to immediate cardiac decompensation. Therefore, the nurse must prioritize assessing for and intervening on the serum calcium level of 6.2 mg/dL first, as it signals an imminent risk of fatal arrhythmia . Early recognition of this specific metabolic abnormality as the most immediately life-threatening component of TLS is crucial for preventing serious complications and improving patient outcomes .References (research sources)

- [1]Tumor Lysis Syndrome in Solid and Hematologic Malignancies: A Guide for Early Detection and Intervention.Research articleMathew S, Bourgeois J. (2025) · DOI: 10.1188/25.cjon.502-507

## 임상 시나리오

Tumor Lysis Syndrome: Identifying the Immediate ThreatPrioritizing life-threatening electrolyte derangements
In Tumor Lysis Syndrome, all metabolic derangements are critical, but severe hypocalcemia (here, 6.2 mg/dL) demands the most immediate intervention. The rapid binding of calcium with excess phosphorus creates calcium-phosphate crystals, causing a precipitous drop in ionized calcium.

This directly destabilizes myocardial membranes, leading to a prolonged QT interval and a high risk of Torsades de Pointes, a fatal ventricular arrhythmia. Cardiac monitoring and intravenous calcium replacement are the top priorities to prevent cardiac arrest.

CautionWhile hyperkalemia is also cardiotoxic, profound hypocalcemia poses the most acute and immediate arrhythmia risk in the context of TLS. Do not delay treatment to first address other lab values.

## 핵심 개념

- **Tumor Lysis Syndrome** — This is a life-threatening metabolic complication that occurs when tumor cells are rapidly destroyed in large numbers, releasing intracellular contents (potassium, phosphate, nucleic acids) into the bloodstream. It is characterized by hyperuricemia, hyperphosphatemia, hyperkalemia, and hypocalcemia.
- **Hypocalcemia** — A condition where serum calcium levels fall below normal. In TLS, calcium phosphate precipitation due to hyperphosphatemia is the main cause. It can cause neuromuscular irritability (tetany, muscle cramps), laryngospasm, Chvostek/Trousseau signs, and cardiac arrhythmias such as QT interval prolongation.
- **Hyperphosphatemia** — A condition where serum phosphate levels rise above normal. It occurs due to the massive release of intracellular phosphate in TLS and is a major cause of hypocalcemia and renal precipitation (calcium phosphate nephropathy).
- **Hyperkalemia** — A condition where serum potassium levels rise above normal. In TLS, it occurs due to the massive release of intracellular potassium. It can affect the heart muscle, causing muscle weakness, abnormal sensations, ECG changes (tall T waves, wide QRS), and cardiac arrest.
- **Hyperuricemia** — Serum uric acid level elevated above normal. Occurs due to massive breakdown of cellular nucleic acids (purines) in TLS. Uric acid crystals deposit in renal tubules, becoming a major cause of acute kidney injury (AKI).

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