In tumor lysis syndrome, which electrolyte abnormality is commonly observed?

• A. Hyperkalemia
• B. Hypercalcemia
• C. Hyperphosphatemia
• D. Hyponatremia

Answer: (C)

When tumor cells break down rapidly, they spill their intracellular contents into the blood. Phosphate is released in large amounts, so serum phosphate levels rise, causing hyperphosphatemia. This elevation binds calcium, leading to a drop in free calcium (hypocalcemia) and potential calcium phosphate precipitation, especially in the kidneys. Among the given choices, hyperphosphatemia is the most characteristic electrolyte abnormality seen in tumor lysis syndrome. Remember, while potassium can also rise and hyponatremia is not a hallmark, the rise in phosphate directly reflects the massive cell lysis that defines this condition and informs management, including hydration, uric acid–lowering therapy, and monitoring and treating electrolyte disturbances.