The body contains 22-26 grams of magnesium (1,000 mmols). Of this, 60% is located in bone (30% of which is exchangeable and functions as a reservoir to stabilize the serum concentration), 20% in skeletal muscle,  19% in other soft tissues, and < 1% in extracellular fluid. For this reason, blood levels of magnesium are not an adequate means of establishing the total amount of available magnesium. The normal total serum magnesium ranges between 1.7-2.3 mg/dl (0.70 and 1.10 mmol/L). Around 20% of this is protein bound, 65% is ionized and the rest is bound with various anions/chelators (i.e. ATP, ADP, proteins, bicarbonate and citrate). Of the protein bound fraction, 60–70% is associated with albumin and the rest is bound to globulins. Around 5-10% of magnesium is free and is essential in regulating intracellular magnesium. Magnesium is a cofactor in more than 300 enzyme regulated reactions. Most importantly forming and using ATP, i.e. kinase. There is a direct effect on sodium- (Na), potassium- (K) and calcium (Ca)channels. Serum ionized magnesium concentration (0.54–0.67 mmol/L) and is narrower than calcium. Acid base disturbances (metabolic acidosis or alkalosis) have little effect on the distribution of serum magnesium. The concentration of magnesium in CSF is around 1.1 mmol/L (55% is free and 45% is bound with other compounds). The higher ultrafiltrable magnesium in CSF compared to serum is due to active transport of magnesium across the blood-brain barrier.
Hypomagnesemia pathophysiology
Hypokalemia pathophysiology
Hyperkalemia pathophysiology
Hyperkalemia risk factors
Hyponatremia pathophysiology
Renal tubular acidosis risk factors
Hypernatremia pathophysiology
Hypomagnesemia risk factors