# A nurse is assessing a 58-year-old patient with acute myeloid leukemia who has been receiving chemotherapy. Which assessment finding would be the MOST critical indicator of tumor lysis syndrome requiring immediate intervention?

> source: MyMerci (mymerci.kr)  
> url: https://mymerci.kr/pages/nclex_q.php?qn_id=540758  
> language: ko  
> subject: Adult Health

## 문제

A nurse is assessing a 58-year-old patient with acute myeloid leukemia who has been receiving chemotherapy. Which assessment finding would be the MOST critical indicator of tumor lysis syndrome requiring immediate intervention?

## 보기

1. Serum uric acid level of 8.5 mg/dL (normal: 3.5-7.2 mg/dL)
2. Serum potassium level of 6.8 mEq/L (normal: 3.5-5.0 mEq/L) **✔ 정답**
3. Serum phosphorus level of 5.2 mg/dL (normal: 3.0-4.5 mg/dL)
4. Serum calcium level of 7.8 mg/dL (normal: 9.0-10.5 mg/dL)

**정답: 2**

## 해설

Hyperkalemia (K+ 6.8 mEq/L) is the most critical TLS finding due to risk of fatal arrhythmias. Other electrolyte imbalances are serious but less immediately life-threatening.

## 심화 해설

Understanding Tumor Lysis Syndrome (TLS)

Tumor lysis syndrome is an oncologic emergency that occurs when massive numbers of malignant cells are rapidly destroyed, releasing their intracellular contents—potassium, phosphate, and nucleic acids (which are metabolized to uric acid)—into the bloodstream. This rapid release overwhelms the body's homeostatic mechanisms, leading to a characteristic quartet of metabolic derangements: hyperkalemia, hyperphosphatemia, hypocalcemia (secondary to calcium-phosphate precipitation), and hyperuricemia. While all these abnormalities can cause significant morbidity, the immediate threat to life stems from the cardiac effects of severe electrolyte disturbances [1,2].

Prioritizing the Findings: The Cardiac Threat

The core of this question lies in recognizing the most immediately life-threatening complication. The simulation literature emphasizes that prompt recognition and treatment of hyperkalemia-induced arrhythmias is vital, as these can be life-threatening and lead to multi-organ failure if untreated [2]. Let's analyze each laboratory value in this context:

Analysis of Options

- **Serum uric acid level of 8.5 mg/dL:** This is elevated, confirming the diagnosis of TLS. Hyperuricemia can lead to acute kidney injury from urate crystal deposition in the renal tubules. While serious, renal failure develops over hours to days, not minutes. The use of agents like rasburicase is effective for normalizing uric acid levels and preventing these complications [3]. This finding requires treatment but is not the most immediate cardiac threat.

- **Serum potassium level of 6.8 mEq/L:** This is a critically high value. Severe hyperkalemia directly destabilizes cardiac myocyte resting membrane potentials, reducing the threshold for depolarization. This creates a high risk for life-threatening tachyarrhythmias, including ventricular tachycardia and ventricular fibrillation, which can result in cardiac arrest [2]. This represents an immediate, minute-to-minute threat to life and demands the most urgent intervention.

- **Serum phosphorus level of 5.2 mg/dL:** This is elevated. The primary danger of hyperphosphatemia in TLS is its reciprocal relationship with calcium. As phosphate rises, it binds with calcium to form insoluble calcium-phosphate crystals, which can deposit in tissues, including the kidneys, causing hypocalcemia and further renal damage. The cardiac effects are secondary to the resultant hypocalcemia.

- **Serum calcium level of 7.8 mg/dL:** This is low, a direct consequence of the elevated phosphate. Hypocalcemia can cause neuromuscular irritability (tetany, paresthesias), prolonged QT interval, and potentially cardiac arrhythmias. However, the arrhythmia risk from hypocalcemia is generally less acutely catastrophic than the risk of fatal arrhythmias from severe hyperkalemia at a level of 6.8 mEq/L.

Clinical Reasoning and Priority Setting

Using the "ABC" (Airway, Breathing, Circulation) priority framework, the finding with the most direct and immediate impact on circulation is the severe hyperkalemia. A potassium level above 6.5 mEq/L constitutes a medical emergency due to the imminent risk of fatal cardiac arrhythmias. The case reports on TLS consistently highlight that severe hyperkalemia, if untreated, may lead to renal failure, arrhythmias, or multi-organ failure, with the cardiac complications being the most proximate cause of death [2,4]. While the other electrolyte abnormalities (hyperuricemia, hyperphosphatemia, and hypocalcemia) are all characteristic of TLS and require management, none carry the same immediate, lethal cardiac risk as a potassium level of 6.8 mEq/L.

References (research sources)

- [2]Recognition and Management of Hyperkalemia-Induced Tachyarrhythmia in Pediatric Spontaneous Tumor Lysis Syndrome: A Simulation Case.Research articleSoliman YH, Kochhar M, Petrone G, Wing R, Sojar SH. (2026) · DOI: 10.7759/cureus.107494

- [3]The Use of Single Dose of Rasburicase for the Prophylaxis and Treatment of Tumor Lysis Syndrome in Pediatric Patients: A Narrative Review.Research articleLee AC. (2025) · DOI: 10.3390/hematolrep17060071

## 임상 시나리오

Tumor Lysis Syndrome: Emergency PrioritizationHyperkalemia is the most immediate lethal threat
In Tumor Lysis Syndrome, rapid cell breakdown releases intracellular contents. The resulting hyperkalemia (K+ > 5.0 mEq/L) can cause fatal cardiac arrhythmias within minutes, making it the highest priority over hyperuricemia, hyperphosphatemia, or hypocalcemia.

Immediate interventions for severe hyperkalemia (e.g., K+ 6.8 mEq/L) include administering IV calcium gluconate to stabilize the myocardium, followed by shifting potassium intracellularly with IV regular insulin and dextrose.

CautionDo not delay cardiac monitoring and emergency treatment for hyperkalemia to address other TLS abnormalities like uric acid. A serum potassium level above 6.5 mEq/L constitutes a critical value requiring immediate action to prevent asystole or ventricular fibrillation.

## 핵심 개념

- **Tumor Lysis Syndrome** — An oncologic emergency caused by rapid tumor cell destruction releasing intracellular contents, leading to hyperkalemia, hyperphosphatemia, hypocalcemia, and hyperuricemia.
- **Hyperkalemia** — Elevated serum potassium (>5.0 mEq/L) that destabilizes cardiac cell membranes, risking life-threatening arrhythmias like ventricular fibrillation or asystole.
- **Cardiac Arrhythmia** — An abnormal heart rhythm; in TLS, severe hyperkalemia is the primary cause of immediate fatal arrhythmias requiring urgent correction.
- **Prioritization** — The nursing process of ranking patient needs by acuity; airway, breathing, and circulation (including lethal arrhythmias) take precedence over other organ dysfunction.

## 같은 주제 문제

- [A nurse is assessing a 45-year-old patient with acute lymphoblastic leukemia who was admit…](https://mymerci.kr/pages/nclex_q.php?qn_id=540756)
- [A nurse is caring for a patient with acute lymphoblastic leukemia who suddenly develops se…](https://mymerci.kr/pages/nclex_q.php?qn_id=540757)
- [A nurse is caring for a patient with acute lymphoblastic leukemia who develops tumor lysis…](https://mymerci.kr/pages/nclex_q.php?qn_id=540759)
- [A nurse is caring for a patient with acute lymphoblastic leukemia who develops tumor lysis…](https://mymerci.kr/pages/nclex_q.php?qn_id=540760)
- [A nurse is caring for a 45-year-old patient with acute lymphoblastic leukemia who received…](https://mymerci.kr/pages/nclex_q.php?qn_id=540761)
- [A nurse is caring for a patient with acute leukemia who suddenly develops severe shortness…](https://mymerci.kr/pages/nclex_q.php?qn_id=540762)
- [A nurse is caring for a 35-year-old patient with Hodgkin lymphoma who reports progressive …](https://mymerci.kr/pages/nclex_q.php?qn_id=540763)
- [A nurse is caring for a patient with acute leukemia who develops sudden onset of severe he…](https://mymerci.kr/pages/nclex_q.php?qn_id=540764)

---

More free questions: [기출문제](https://mymerci.kr/)

_학습 참고용입니다. 실제 임상은 최신 지침과 소속 기관 프로토콜을 따르세요._