Type of test Blood
Normal findings
Adult: 1.3-2.1 mEq/L or 0.65-1.05 mmol/L (SI units)
Child: 1.4-1.7 mEq/L
Newborn: 1.4-2 mEq/L
Possible critical values: < 0.5 mEq/L or > 3 mEq/L
Test explanation and related physiology
Most organ functions also depend on magnesium. It is especially important to monitor magnesium levels in cardiac patients. Low magnesium may increase cardiac irritability and aggravate cardiac arrhythmias. Hypermagnesemia retards neuromuscular conduction and is demonstrated as cardiac conduction slowing (widened PR and Q-T intervals, with wide QRS).
As intracellular elements, potassium, magnesium, and calcium (in order of quantity) are intimately tied together in maintaining a neutral intracellular electrical charge. That is why it is hard to maintain a normal potassium level when a patient has low magnesium blood levels.
Magnesium deficiency occurs in patients who are malnourished. Toxemia of pregnancy is also believed to be associated with reduced magnesium levels. Magnesium testing is used to monitor magnesium replacement therapy.
Increased magnesium levels most commonly are associated with ingestion of magnesium-containing antacids. Because most of the serum magnesium is excreted by the kidneys, chronic renal diseases cause elevated magnesium levels.
Interfering factors
• Hemolysis should be avoided when collecting this specimen.
* Drugs that increase magnesium levels include aminoglycoside antibiotics, antacids, calcium-containing medications, laxatives, lithium, loop diuretics, and thyroid medication. Drugs that decrease magnesium levels include some antibiotics, diuretics, and insulin.
Procedure and patient care
• See inside front cover for Routine Blood Testing.
• Fasting: no
• Blood tube commonly used: red
Abnormal findings
Increased levels
- Renal insufficiency
- Uncontrolled diabetes
- Addison disease
- Hypothyroidism
- Ingestion of magnesium containing antacids or salts
Decreased levels
- Malnutrition
- Malabsorption
- Hypoparathyroidism
- Alcoholism
- Chronic renal disease
- Diabetic acidosis
