Hypermagnesemia refers to an excess amount of magnesium in the bloodstream. It is rare and is usually caused by renal failure or poor kidney function.

Magnesium is a mineral the body uses as an electrolyte, meaning it carries electric charges around the body when dissolved in the blood.

Magnesium has a role in bone health, cardiovascular function, and neurotransmission, among other functions. Most magnesium is stored in the bones.

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Usually, very little magnesium is found in the blood. When magnesium levels are particularly high, it is known as hypermagnesemia.

Hypermagnesemia is rare and occurs when too much magnesium circulates in the blood.

In healthy people, very little magnesium circulates in the blood. The gastrointestinal (gut) and renal (kidney) systems regulate and control how much magnesium the body absorbs from food and how much is excreted in urine.

These systems control how much magnesium the body absorbs from food and how much is excreted in urine.

A healthy body maintains a level of 1.7 to 2.3 milligrams per deciliter (mg/dL) of magnesium at all times.

A high magnesium level is 2.6 mg/dL or above.

Most cases of hypermagnesemia occur in people who have kidney failure. Hypermagnesemia occurs because the process that keeps the levels of magnesium in the body at normal levels does not work properly in people with kidney dysfunction and end-stage liver disease.

When the kidneys do not work properly, they are unable to get rid of excess magnesium, and this makes the person more susceptible to a build-up of the mineral in the blood.

Some treatments for chronic kidney disease, including proton pump inhibitors, can increase the risk of hypermagnesemia. Malnourishment and alcoholism are additional risk factors in people with chronic kidney disease.

Other causes

It is rare for someone who has normal kidney function to develop hypermagnesemia. If a person with healthy kidney function does develop hypermagnesemia, the symptoms are usually mild.

Other causes of hypermagnesemia include:

  • lithium therapy
  • hypothyroidism
  • Addison's disease
  • milk-alkali syndrome
  • drugs containing magnesium, such as some laxatives and antacids
  • familial hypocalciuric hypercalcemia

The condition can also develop in someone who has been treated for a drug overdose with magnesium-containing cathartics.

Women taking magnesium as a treatment for preeclampsia may also be at risk if their dose is too high.

The symptoms of hypermagnesemia include:

Particularly high levels of magnesium in the blood can lead to heart problems, difficulty breathing, and shock. In severe cases, it can result in coma.

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A blood test can be carried out to diagnose hypermagnesemia by measuring magnesium levels in the blood.

Hypermagnesemia is diagnosed using a blood test. The level of magnesium found in the blood indicates the severity of the condition.

A normal level of magnesium is between 1.7 and 2.3 mg/dL. Anything above this and up to around 7 mg/dL can cause mild symptoms, including flushing, nausea, and headache.

Magnesium levels between 7 and 12 mg/dL can impact the heart and lungs, and levels in the upper end of this range may cause extreme fatigue and low blood pressure.

Levels above 12 mg/dL can lead to muscle paralysis and hyperventilation. When levels are above 15.6 mg/dL, the condition may result in a coma.

The first step in treating hypermagnesemia is identifying and stopping the source of extra magnesium.

An intravenous (IV) calcium supply is then used to reduce symptoms such as impaired breathing, irregular heartbeat, and hypotension, as well as the neurological impact.

Intravenous calcium, diuretics, or water pills may also be used to help the body get rid of excess magnesium.

People with renal dysfunction or those who have had a severe magnesium overdose may require dialysis if they are experiencing kidney failure, or if magnesium levels are still rising after treatment.

People with underlying kidney issues are at risk of developing hypermagnesemia because their kidneys may not be able to excrete enough magnesium.

Avoiding medications that contain magnesium can help prevent complications. This includes some over-the-counter antacids and laxatives.

Doctors are advised to test for hypermagnesemia in anyone with underperforming kidneys who experiences the associated symptoms.

If diagnosed early, hypermagnesemia is usually treatable. If renal function is normal, the kidneys can excrete the excess magnesium quickly once the source has been identified and stopped.

Severe cases, especially if diagnosed late, can be harder to treat in those with damaged kidneys. Dialysis and intravenous calcium can stop symptoms quickly, however.

Older people with renal dysfunction have a higher risk of developing severe complications. Critically ill people already admitted to hospital have a higher rate of death if diagnosed with hypermagnesemia.