Magnesium: Physiology, Laboratory Pitfalls, and Clinical Implications

Introduction: Magnesium as the Body’s Silent Workhorse

Magnesium is the body’s quiet workhorse: a predominantly intracellular mineral that stabilizes ATP (the cell’s energy currency), tunes ion channels, and modulates hundreds of enzymes involved in nerve transmission, muscle contraction, DNA/RNA synthesis, and heart rhythm. Only about one percent of total body magnesium is in the bloodstream; roughly sixty percent is in bone and the rest in soft tissues. That small serum fraction is what labs report, so a normal result does not always reflect total body stores. Typical adult reference ranges are about 1.7–2.2 mg/dL (0.70–0.95 mmol/L), which corresponds to roughly 1.4–2.0 mEq/L. Because so little magnesium circulates freely, serum magnesium can be deceptively normal in early depletion, which is why clinical context, and sometimes urine testing, matters.

Distribution and Absorption of Magnesium

The body keeps magnesium in balance through intestinal absorption, renal handling, and exchange with bone. Most absorption occurs in the small intestine by…