Hypermagnesemia (High Blood Magnesium)

What is hypermagnesemia?

Hypermagnesemia is the medical term for high magnesium levels in the blood. It is an uncommon condition because the kidney is very proficient in getting rid of excess magnesium from the body. Hypermagnesemia is unlikely to occur unless magnesium is being administrated in a person with kidney failure. This may be in the form of supplements or magnesium-containing medication. High levels of magnesium in the body is usually not immediately apparent unless the levels are excessively high. It can lead to severe symptoms and even death if left untreated.

Effects of High Blood Magnesium

Magnesium is one of the essential minerals needed by the body. About half of all magnesium is within the bones and only about 1% is circulating in the bloodstream. Magnesium is needed for various functions throughout the body and is an integral part of homeostasis – the natural balance in the body that maintains health. The kidney is the main organ that regulates the amount of circulating magnesium. A deficiency of magnesium is known as hypomagnesemia. When magnesium is deficient it leads to a host of effects particularly of the muscles, nerves, bones, blood glucose, heart rhythm, blood pressure and urine.

Similarly hypermagnesemia (high blood magnesium) can have a host of adverse effects in the body. The effects are not always apparent unless there is associated low blood calcium (hypocalcemia), high blood potassium (hyperkalemia) and high urea levels (uremia). These other metabolic disturbances often occur in kidney failure which is the most common cause of hypermagnesemia. The main effects of high blood magnesium involves the nerve and muscle activity, heart conduction system, blood pressure and calcium levels in the blood. Severe hypermagnesemia can stop the heart from beating.

Symptoms of High Levels of Magnesium

Most of the symptoms of excess magnesium levels is a result of disturbance of the nerve and muscle activity primarily when it affects the cardiovascular system. However, hypermagnesemia has a host of effects on the body. The symptoms seen with hypermagnesemia may not be due to the excessively high magnesium levels alone. Other disturbances of calcium, potassium and urea levels also contributes to the clinical presentation.

The signs and symptoms of hypermagnesemia includes :

  • Low blood pressure (hypotension).
  • Irregular heart beat (arrhythmia).
  • Low heart rate (bradycardia).
  • Flushing of the skin.
  • Slow or difficult breathing.
  • Facial paresthesia.
  • Muscle weakness.
  • Decreased tendon reflexes.
  • Disturbances in blood clotting.
  • Constipation (paralytic ileus).
  • Nausea.
  • Vomiting.
  • Headache.
  • Lethargy.
  • Sleepiness.

Severe hypermagnesemia may lead to :

  • Temporary cessation of breathing (apnea).
  • Complete heart block and cardiac arrest.
  • Fixed and dilated pupils.
  • Drowsiness.

Causes of Hypermagnesemia

Most cases of hypermagnesemia are seen with kidney failure. However, there are other less common causes which also need to be considered especially in patients with normal kidney function.

Kidney Failure

The level of magnesium in the bloodstream is determined largely by the kidney. Tubular reabsorption is a process where the kidneys remove certain substances that have entered the tubule of the nephron. Without reabsorption, these substances would be eliminated from the body via the urine. Most of the magnesium in the tubule is reabsorbed from the loop of Henle. If the body needs to eliminate excess magnesium, reabsorption can be reduced. Conversely, if magnesium was needed, then the reabsorption would be increased.

The kidney is very effective in eliminating magnesium which is one of the reasons why hypermagnesemia is not a common electrolyte disturbance. In fact the magnesium reabsorption can be reduced to almost negligible amounts ensuring the majority of the magnesium is excreted in the urine. However, in kidney failure various renal processes are affected. Hypermagnesemia is more likely to occur in end-stage renal disease during periods of very low urine output (oliguria).

However, hypermagnesemia may not occur even with renal failure. Even if present it is usually mild. It is mainly when there is concomitant administration of magnesium, usually unintentionally in the form of magnesium containing medication, that hypermagnesemia arises in patients with kidney failure. This includes medication such as antacids, certain laxatives and lithium. Patients undergoing regular dialysis are less likely to develop hypermagnesemia.

Other Causes

There are several other causes of high blood magnesium such as :

  • Addison disease
  • Depression
  • Excessive magnesium intake – supplements or magnesium-containing medication.
  • Hemolytic anemia
  • Hypothyroidism
  • Familial hypocalciuric hypercalcemia

Foods High In Magnesium

Although an excessive intake of magnesium from food is unlikely, it is worth considering in patients with impaired kidney function who are consuming large amounts of certain foods. Some of these foods are often termed ‘health foods’ and the patient may be consuming it in large amounts to derive the health benefit without realizing the impact of their dietary habits. The ten foods with the highest amount of magnesium in descending order includes :

  • Wheat bran
  • Almonds
  • Spinach
  • Cashews
  • Soybeans
  • Wheat germ
  • Mixed nuts
  • Bran flakes
  • Shredded wheat
  • Oatmeal

Blood Magnesium Tests and Readings

Hypermagnesemia should be diagnosed with the use of diagnostic investigations like a blood test. Although the symptoms of hypermagnesemia in a patient with known kidney disease may raise the suspicion of this electrolyte imbalance, definite diagnostic testing is necessary. The normal blood plasma readings in a healthy adult usually ranges from 1.7 to 2.3mg/dL (0.7 to 0.96 mmol/L).

  • Mild : 4.8 to 7.2 mg/dL (2 to 3 mmol/L).
  • Moderate : 7.2 to 12 mg/dL (3 to 5 mmol/L).
  • Severe : above 12 mg/dL (5 mmol/L)

Hypermagnesemia Treatment

Mild hypermagnesemia usually does not require any treatment. The contributing agent, either medication, supplements or foods, should be discontinued orĀ  the intake reduced. Even mild hypermagnesemia that is acute in kidney failure patients may not require therapy if the patient is passing out normal amounts of urine or undergoing dialysis. However, if no specific therapy is being undertaken then it is important to regularly monitor the blood magnesium levels to ensure that it is decreasing at a consistent rate.

Moderate to severe hypermagnesemia requires treatment. The following therapeutic measures may be undertaken for hypermagnesemia :

  • Calcium gluconate administration, usually intravenously, to counteract the effects of high magnesium levels.
  • Diuretics to increase urination but should only be used in patients with normal kidney function.
  • Dialysis for patients with impaired kidney function.

Hypermagnesemia rarely occurs on its own with there being some disturbance in the calcium and potassium levels. Therefore other therapeutic measures may also be necessary to correct these electrolyte abnormalities.

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