Magnesium, Blood

Magnesium, Blood is a topic covered in the Davis's Lab & Diagnostic Tests.

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Synonym/Acronym:
Mg2+.

Rationale
To assess electrolyte balance related to magnesium levels to assist in diagnosis, monitoring diseases, and therapeutic interventions such as hemodialysis, preeclampsia, and eclampsia.

Patient Preparation
There are no food, fluid, activity, or medication restrictions unless by medical direction.

Normal Findings
Method: Spectrophotometry.

AgeConventional UnitsSI Units (Conventional Units × 0.4114)
Newborn1.7–2.5 mg/dL0.7–1 mmol/L
Child1.7–2.3 mg/dL0.7–0.95 mmol/L
Adult1.6–2.2 mg/dL0.66–0.91 mmol/L
Pregnant female
First and second trimester1.5–2.2 mg/dL0.63–0.91 mmol/L
Third trimester1.1–2.2 mg/dL0.46–0.91 mmol/L

Critical Findings and Potential Interventions

Adults

  • Less than 1.2 mg/dL (SI: Less than 0.5 mmol/L)
  • Greater than 4.9 mg/dL (SI: Greater than 2 mmol/L)

Children

  • Less than 1.2 mg/dL (SI: Less than 0.5 mmol/L)
  • Greater than 4.3 mg/dL (SI: Greater than 1.8 mmol/L)

Timely notification to the requesting health-care provider (HCP) of any critical findings and related symptoms is a role expectation of the professional nurse. A listing of these findings varies among facilities.

Consideration may be given to verification of critical findings before action is taken. Policies vary among facilities and may include requesting immediate recollection and retesting by the laboratory or retesting using a rapid point-of-care testing instrument at the bedside, if available.

Symptoms such as tetany, weakness, dizziness, tremors, hyperactivity, nausea, vomiting, and convulsions occur at decreased (less than 1.2 mg/dL [SI: less than 0.5 mmol/L]) concentrations. Electrocardiographic (ECG) changes (prolonged P-R and Q-T intervals; broad, flat T waves; and ventricular tachycardia) may also occur. Treatment may include IV or oral administration of magnesium salts, monitoring for respiratory depression and areflexia (IV administration of magnesium salts), and monitoring for diarrhea and metabolic alkalosis (oral administration to replace magnesium).

Respiratory paralysis, decreased reflexes, and cardiac arrest occur at grossly elevated (greater than 15 mg/dL [SI: greater than 6.2 mmol/L]) levels. ECG changes, such as prolonged P-R and Q-T intervals, and bradycardia may be seen. Toxic levels of magnesium may be reversed with the administration of calcium, dialysis treatments, and removal of the source of excessive intake.

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