RBC Magnesium

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Latest Edit: Hector 2014-03-24 (EDT)

See Also Lab Tests

The RBC magnesium test is used to evaluate the level of magnesium in the blood. This in turn can help to determine the cause of abnormal calcium and/or potassium levels. The test is usually conducted when a patient presents with symptoms such as weakness, irritability, cardiac arrhythmia, nausea, and/or diarrhea that may be due to too much or too little magnesium.[1], [2]


  • Magnesium is a mineral that is vital for energy production, muscle contraction, nerve function, and the maintenance of strong bones.
  • It is obtained through diet, absorbed by the small intestine and colon, and stored in the bones, cells, and tissues.
  • Normally, only 1% of total body magnesium is present in the blood.

Patient Preparation

  • Overnight fasting may be required.
  • Factors which can cause increased levels:
  • Drugs: lithium, aspirin, thyroid medication, some antibiotics, and products that contain magnesium
  • Factors which can cause decreased levels:
  • pregnancy (particularly during the second and third trimesters)
  • Drugs: digoxin, cyclosporin, diuretics, insulin, some antibiotics, laxatives, and phenytoin

Clinical Implications

High levels indicate:

Low levels indicate:

  • Malabsorption
  • Malnutrition or low dietary intake
  • Prolonged diarrhea
  • Gastrointestinal disorders
  • Uncontrolled diabetes
  • Hypoparathyroidism
  • Long-term diuretic use
  • Post surgery
  • Severe burns
  • Toxemia or pregnancy

Associated Tests


  1. Pagana Kathleen D, Pagana Timothy J (2006) Mosby's Manual of Diagnostic and Laboratory Tests, Mosby.
  2. Weatherby Dicken, Ferguson Scott (2002) Blood Chemistry and CBC Analysis: Clinical Laboratory Testing from a Functional Perspective, Bear Mountain.