A magnesium test is used to measure the level of magnesium in the blood (or sometimes urine). Abnormal levels of magnesium are most frequently seen in conditions or diseases that cause impaired or excessive excretion of magnesium by the kidneys or that cause impaired absorption in the intestines. Magnesium levels may be checked as part of an evaluation of the severity of kidney problems and/or of uncontrolled diabetes and may help in the diagnosis of gastrointestinal disorders.
Since a low magnesium blood level can, over time, cause persistently low calcium and potassium levels, it may be checked to help diagnose problems with calcium, potassium, phosphorus, and/or parathyroid hormone – another component of calcium regulation.
Magnesium levels may be measured frequently to monitor the response to oral or intravenous (IV) magnesium supplements and may be ordered, along with calcium and phosphorus testing, to monitor calcium supplementation.
Magnesium testing may be ordered as a follow up to chronically low blood levels of calcium and potassium. It also may be ordered when a person has symptoms that may be due to a magnesium deficiency, such as muscle weakness, twitching, cramping, confusion, cardiac arrhythmias, and seizures.
A health practitioner may order a magnesium level to check for a deficiency as part of an evaluation of malabsorption, malnutrition, diarrhea, or alcoholism. When someone is taking medications that can cause the kidneys to excrete magnesium, testing may be performed as well. When magnesium and/or calcium supplementation is necessary, the level of magnesium in the blood may be checked at intervals to monitor the effectiveness of treatment.
When someone has a kidney disorder or uncontrolled diabetes, a magnesium test may be ordered periodically, along with kidney function tests such as a BUN and creatinine, to help monitor kidney function and to make sure that the person is not excreting or retaining excessive amounts of magnesium.
Since magnesium is an electrolyte, a magnesium test may be ordered along with other electrolytes such as sodium, potassium, chloride, bicarbonate (or total CO2), calcium, and phosphorus to evaluate a person's electrolyte balance. If magnesium is low, it is not unusual for potassium also to be low.
Magnesium blood levels tend to be decreased in the second and third trimesters of pregnancy.
Normal levels of magnesium do not necessarily reflect total body stores of magnesium. The body attempts to keep blood magnesium levels relatively stable and will release magnesium from bone and tissues to accomplish this. So, the blood level may be normal with early magnesium deficiencies.
Drugs that can increase magnesium levels include lithium, aspirin, thyroid medication, some antibiotics, and products that contain magnesium. Drugs that can decrease magnesium levels include digoxin, cyclosporine, diuretics, insulin, some antibiotics, laxatives, and phenytoin.
This article was last reviewed on December 11, 2013. | This article was last modified on December 11, 2013.
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