Magnesium along with potassium is a major intracellular cation. Mg 2+ is a cofactor of many enzyme systems. Thus, all ATP‑dependent enzymatic reactions require Mg 2+ as a cofactor in the ATP‑magnesium complex. Approximately 69 % of magnesium ions are stored in bone. The rest are part of the intermediary metabolism, about 70 % being present in free form while the other 30 % is bound to proteins (especially albumin), citrates, phosphate, and other complex formers. The Mg 2+ serum level is kept constant within very narrow limits (0.65‑1.05 mmol/L). Regulation takes place mainly via the kidneys, especially via the ascending loop of Henle.
This assay is used for diagnosing and monitoring hypomagnesemia (magnesium deficiency) and hypermagnesemia (magnesium excess). Numerous studies have shown a correlation between magnesium deficiency and changes in calcium‑, potassium‑ and phosphate‑homeostasis which are associated with cardiac disorders such as ventricular arrhythmias that cannot be treated by conventional therapy, increased sensitivity to digoxin, coronary artery spasms, and sudden death. Additional concurrent symptoms include neuromuscular and neuropsychiatric disorders. Hypermagnesemia is found in acute and chronic renal failure, magnesium excess, and magnesium release from the intracellular space