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
