What does the Magnesium (Total Serum Magnesium) test measure?

Why is Magnesium (Total Serum Magnesium) measured?

Serum magnesium is the validated, guideline-anchored test for detecting acute magnesium disturbance and is the appropriate measure in acute care, drug monitoring, and the investigation of refractory electrolyte abnormalities. Its recognised limitation is that it samples under 1% of body magnesium and is defended by release from bone and tissue stores, so it typically remains within the reference interval until depletion is substantial and is therefore insensitive to chronic depletion. Because roughly 30% is albumin-bound, total serum magnesium also underestimates the biologically active ionised fraction in hypoalbuminaemia.

Reference ranges

Standard reference

Adults: 1.7–2.2 mg/dL (0.70–0.91 mmol/L)

Functional medicine optimal

Values in the upper half of the reference interval are sometimes cited as favourable in functional medicine, though no standardised optimal threshold exists

Units

mg/dL, mmol/L

Reference ranges vary by laboratory and assay platform. Interpret in context of the issuing laboratory's stated range.