Which of the following lab abnormalities would you most expect in a patient with long-standing hypomagnesemia impairing magnesium-dependent enzymes, and why?

• A. Elevated serum chloride as the hallmark metabolic effect because magnesium is the major extracellular anion that opposes chloride.
• B. Marked hyperthyroidism due to increased enzymatic cleavage of T4 to T3 driven by magnesium excess.
• C. Immediate and isolated hypercalcemia because magnesium deficiency always causes direct mobilization of bone calcium stores independent of PTH status.
• D. Impaired glucose tolerance/insulin resistance and possible dyslipidemia because magnesium-dependent enzymes are required for carbohydrate metabolism and cellular energy homeostasis.

Answer: (D)