Magnesium

The blood magnesium concentration is not usually measured as part of routine blood tests and is ordered when there is a clinical suspicion that the level might be too high or too low. Common reasons to check for a low magnesium level would be chronic diarrhea, alcoholism, diuretic use or chronic protein pump inhibitor for reflux/heartburn/peptic ulcer disease. Less common manifestations of low magnesium would be unexplained low blood potassium, low blood calcium or cardiac arrhythmias.

Patients with severely low magnesium levels should receive intravenous therapy with cardiac monitoring. Oral replacement is appropriate for an asymptomatic patient.

Magnesium is excreted by the kidneys and can rise to toxic levels in renal failure. The body’s reserve of magnesium is stored in the bones but the high levels of magnesium in renal failure is due to dietary magnesium, usually from medications such as antacids or laxatives in usual doses. Patients with renal impairment should not take over the counter medications that contain magnesium.

Medical Trivia: Extremely high blood magnesium in conjunction with very high blood calcium is seen as a unique feature of Dead Sea water poisoning since the Dead Sea contains very high concentrations of both magnesium and calcium.