Like calcium, magnesium may be bound to serum proteins or free (ionized), both together giving the total magnesium concentration.

Measurement: ion-selective electrode (ISE)


The relationship between total and ionized magnesium is not constant in all patients. A low ionized magnesium concentration may be associated with a normal total magnesium.


Factors affecting ionized magnesium levels and its relationship to total magnesium:

(1) low serum albumin and other proteins (binding is pH and concentration dependent)

(2) low pH (ionized levels increase as the pH decreases)


Ionized hypermagnesemia or hypomagnesemiais associated with a higher mortality in ICU patients.


Risk factors for ionized hypomagnesemia:

(1) diuretic or antibiotic therapy

(2) sepsis


Risk factors for hypermagnesemia:

(1) end-stage renal function

(2) magnesium supplements

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