Malignant Hypercalcemia

Malignant hypercalcemia is an oncologic emergency because a rising calcium level can impair cognition, kidney function, muscle strength, gastrointestinal motility, and cardiac conduction. The bedside pattern often begins with polyuria and thirst: excess calcium reduces the kidney’s ability to concentrate urine, causing volume loss. That depletion then lowers renal calcium clearance and can drive the calcium level higher. The cancer may be raising calcium through PTHrP, destroying bone locally, or producing excess calcitriol. Identifying the mechanism helps determine whether the patient needs antiresorptive therapy, glucocorticoids, or both. Severity matters as well. A corrected calcium greater than 14 mg/dL, particularly with confusion, weakness, vomiting, oliguria, or dysrhythmia, requires rapid treatment rather than observation.