Serum vs Intracellular Nutrient Levels

Serum nutrient levels do not reflect intracellular levels, and most of the body's nutrient stores reside inside cells. Approximately 98% of the body's potassium is stored intracellularly, with only 2% circulating in the blood. Approximately 99% of the body's magnesium is stored intracellularly, with only 1% circulating in the blood. A normal serum reading can coexist with severely depleted intracellular nutrient stores.