Which laboratory finding is hallmark of refeeding syndrome?

• A. Hypophosphatemia
• B. Hyperkalemia
• C. Hypercalcemia
• D. Hyponatremia

Answer: (A)

When refeeding after a period of starvation, a surge of insulin drives phosphate into cells to support ATP production and other anabolic processes. This rapid intracellular shift causes a drop in circulating phosphate levels, making low serum phosphate the characteristic finding of refeeding syndrome. Severe hypophosphatemia can lead to energy failure in multiple organs, contributing to weakness, respiratory failure, cardiac dysfunction, hemolysis, and more.

Other electrolyte changes can occur—potassium and magnesium also shift intracellularly, so hypokalemia and hypomagnesemia are common—but they are not the defining, hallmark finding. Hyponatremia can occur due to fluid shifts and other factors, but it is not the defining feature of refeeding syndrome.