Magnesium
Overview
Magnesium measures the concentration of this essential divalent cation primarily involved in enzymatic reactions, neuromuscular transmission, and structural roles in bones and ATP complexes. About 99% of body magnesium resides intracellularly or in bone; serum levels reflect only 1% of total body stores but indicate acute changes in magnesium balance. Low levels indicate hypomagnesemia from malnutrition, renal losses, or gastrointestinal disorders, while high levels suggest renal failure or iatrogenic overdose. Clinically, magnesium assessment guides electrolyte management and arrhythmia treatment.Clinical Use Cases
- Evaluating hypomagnesemia in patients with refractory hypokalemia or hypocalcemia.
- Monitoring critically ill patients receiving diuretics, proton pump inhibitors, or TPN.
- Assessing risk for torsades de pointes and ventricular arrhythmias.
- Guiding magnesium replacement therapy in preeclampsia/eclampsia.
Specimen Types
- Serum.
- Plasma (heparin).
- Whole blood (rarely for intracellular levels).
Measurement Methods
- Colorimetric assay with xylidyl blue.
- Ion-selective electrode.
- Atomic absorption spectroscopy (reference method).
Test Preparation and Influencing Factors
- No fasting required; avoid hemolysis which falsely elevates results.
- Acute blood loss, burns, or pancreatitis cause redistribution hypomagnesemia.
- Proton pump inhibitors, loop diuretics, and amphotericin B increase renal losses.
- Hypercalcemia, hyperaldosteronism, and diabetes mellitus lower serum magnesium.
Synonyms
- Mg.
- Serum magnesium.