Other names: MG

Magnesium is an essential mineral with a variety of different functions in the body; magnesium is found in every cell in the body. Magnesium is important for the function of the nerves, muscle contraction, producing energy and maintaining strong bone tissue. Half of the body’s magnesium supplies are used to form bone; the magnesium is joined with phosphorus and calcium to produce new bone tissue. There are usually very small amounts of magnesium in the blood; magnesium is taken into the body via diet; magnesium rich foods include leafy green vegetables.

Why is the test used?

Irregularities in the levels of magnesium in the blood are usually associated with conditions which affect the function of the kidneys or the absorption of the intestine; the test is usually used to diagnose problems with the intestines and determine the severity of conditions affecting the kidneys.

Magnesium levels may be checked if a patient has low levels of potassium, calcium or phosphorus; if magnesium levels are lower than normal for a prolonged period of time, this can cause levels of other minerals and electrolytes to decrease.

The test is usually ordered when a patient has symptoms of low magnesium levels, including weak muscles, twitching, muscle cramping, irregular heartbeat, seizures and confusion. The test may also be ordered for patients who have low levels of potassium, phosphorus or calcium.

The test may be repeated if a patient has started taking supplements or embarked on a course of treatment; the test result will show if the treatment is working.

Magnesium levels may also be ordered if a patient has problems with their kidneys; the test can be used as a marker for kidney function.

How is the test performed?

The test is carried out by collecting and analysing a sample of the patient’s blood; usually the blood is taken from a vein on the inside of the elbow. A needle is inserted into the blood and the blood is drawn out and collected in a syringe. Once the sample has been collected, it will be bottled, labelled with the patient’s name and sent away to the laboratory for evaluation.

What do the test results show?

Decreased levels of magnesium in the blood may be caused by different factors, including a poor dietary intake, poor absorption of magnesium in the intestine or over-excretion of magnesium by the kidneys. A magnesium deficiency may be caused by:

  • Low magnesium intake: either through a poor diet or as a result of alcoholism
  • Uncontrolled diabetes
  • Gastrointestinal conditions
  • After surgery
  • Underactive parathyroid gland
  • Prolonged use of diuretic medications

Increased levels of magnesium in the blood may be associated with:

  • Overactive parathyroid gland
  • Addison’s disease
  • Kidney failure
  • Dehydration
  • Underactive thyroid gland

Magnesium concentration in the blood may be lower during the second and third trimesters of pregnancy.

Specific Blood Tests

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