Disorders of Calcium and Phosphate Metabolism Practice Test

Magnesium is a crucial cofactor for both PTH secretion and PTH signaling at target tissues. When magnesium is low, the parathyroid gland struggles to release PTH and the kidneys and bones don’t respond properly to PTH. This creates hypocalcemia that won’t correct just by giving calcium or restricting phosphate. Replenishing magnesium restores normal PTH release and action, allowing calcium to rise toward normal and phosphate handling to improve. Clinically, this means treating with magnesium repletion (often IV magnesium sulfate for acute/severe cases) is the essential step. Once magnesium is corrected, calcium supplementation can be adjusted as needed, but the foundational intervention is repleting magnesium. Other options, like using calcimimetics, would further suppress PTH and worsen calcium levels, and phosphate restriction alone doesn’t address the underlying Mg deficiency or PTH axis.