Laboratory Tests for Tumor Lysis Syndrome
Laboratory TLS is diagnosed by the presence of two or more abnormal serum values—hyperuricemia, hyperkalemia, hyperphosphatemia, and hypocalcemia—occurring within three days before or seven days after starting anticancer treatment. 1
Core Laboratory Panel
The essential laboratory tests for diagnosing and monitoring TLS include:
- Uric acid: Elevated if increased by >25% from baseline or reaching ≥476 mmol/L (8 mg/dL) 1
- Potassium: Elevated if increased by >25% from baseline or reaching ≥6.0 mmol/L (6 mEq/L) 1
- Phosphorus: Elevated if increased by >25% from baseline or reaching ≥1.45 mmol/L (4.5 mg/dL) in adults or ≥2.1 mmol/L (6.5 mg/dL) in children 1
- Calcium: Decreased if reduced by >25% from baseline or reaching ≤1.75 mmol/L (7 mg/dL) 1
- Creatinine and BUN: To assess renal function, as clinical TLS requires eGFR ≤60 mL/min 1
- LDH: Marker of cell turnover and tumor burden 2
- Sodium: For comprehensive electrolyte assessment 2
Monitoring Frequency Based on Risk
High-Risk Patients (Before TLS Develops)
Monitor LDH, uric acid, sodium, potassium, creatinine, BUN, phosphorus, and calcium every 12 hours for the first three days, then every 24 hours subsequently. 3, 2
Established TLS Patients
Monitor the following parameters every 6 hours for the first 24 hours, then daily thereafter: 3, 2
- Vital signs (heart rate, blood pressure, urine output, respiratory rate) 3
- Serum uric acid level 3
- Serum electrolytes (phosphate, calcium, potassium) 3
- Renal function (serum creatinine, BUN, urine pH and osmolality, urine specific gravity) 3
Additional parameters to assess every 24 hours include: 3
- Complete blood count 3
- Serum LDH 3
- Albumin 3
- Serum osmolality 3
- Blood gases and acid-base equilibrium 3
- Electrocardiogram 3
- Body weight 3
Renal Function Assessment
Calculate eGFR using either the MDRD formula or Cockroft-Gault equation to determine if clinical TLS criteria are met (eGFR ≤60 mL/min). 1, 2 This is critical because clinical TLS—which carries significantly higher morbidity and mortality—requires laboratory TLS plus at least one clinical complication: renal failure, cardiac arrhythmias, or seizures. 1, 4
Critical Pitfalls to Avoid
Do not use calcium gluconate to correct mild hypocalcemia, as it increases tissue and renal calcium phosphate precipitation. 3, 2 This common error can worsen renal injury.
Ensure proper sample handling for uric acid measurements in patients receiving rasburicase. 5 Rasburicase continues to degrade uric acid in blood samples at room temperature, potentially causing falsely low readings. Samples should be placed immediately on ice and processed rapidly.
Monitor urine output closely, maintaining at least 100 mL/hour in adults (3 mL/kg/hour in children <10 kg). 3 Measurement of urine osmolality and fractional excretion of sodium helps define hydration status. 3
Clinical Context
The Cairo-Bishop classification system, referenced by the European Hematology Association, provides the standardized framework for these diagnostic criteria. 1, 6 While laboratory TLS occurs in up to 42% of patients with hematologic malignancies, clinically significant TLS develops in only 3-6% of cases. 4, 5 This distinction is crucial because laboratory abnormalities alone may not require aggressive intervention, whereas clinical TLS represents a true oncologic emergency requiring immediate treatment including possible hemodialysis. 6, 7