What is the most serious complication of hyperphosphatemia?

• A. Metastatic and vascular calcification of non-skeletal tissues
• B. Hypocalcemia
• C. Hyperkalemia
• D. Metabolic alkalosis

Answer: (A)

Elevated phosphate increases the calcium-phosphate product, promoting deposition of calcium phosphate in soft tissues, especially in the vasculature. This metastatic calcification stiffens and damages blood vessels, raising cardiovascular risk and mortality—a more dangerous outcome than the accompanying hypocalcemia. While hypocalcemia can cause symptoms, the widespread vascular and soft-tissue calcification that results from hyperphosphatemia is the most severe complication. Hyperkalemia and metabolic alkalosis are not direct consequences of high phosphate, so they don’t fit as the primary dangerous outcome here.