A Rare Case of Pseudohypercalcemia Associated with Multiple Myeloma.

We report a rare case of pseudohypercalcemia associated with multiple myeloma in a 77-year-old woman. Despite elevated albumin-corrected calcium levels (12.6 mg/dL), ionized calcium levels remained normal (1.25 mmol/L). Differential diagnoses excluded common causes of hypercalcemia, and the findings suggested calcium binding to negatively charged immunoglobulins and confirmed pseudohypercalcemia due to IgG-type myeloma. Treatment with isatuximab plus dexamethasone normalized albumin-corrected calcium levels as IgG levels decreased. This report highlights the importance of recognizing pseudohypercalcemia to prevent misdiagnosis of true hypercalcemia due to myeloma. Measuring ionized calcium levels is crucial for accurate diagnosis when hypercalcemia is suspected without corresponding clinical symptoms.