Davis's Lab & Diagnostic Tests
Magnesium, Blood, and Urine
General
Synonym/Acronym:
Mg2+.
Rationale
Blood: To assess electrolyte balance related to magnesium levels in general, to assist in diagnosis and monitoring of diseases; providing and monitoring therapeutic interventions especially for specific subsets of patients such as those receiving hemodialysis and those being treated for pre-eclampsia and eclampsia. Urine: To assess magnesium levels related to renal function.
Patient Preparation
There are no food, fluid, activity, or medication restrictions unless by medical direction. For urine studies, usually a 24-hr urine collection is ordered. As appropriate, provide the required urine collection container and specimen collection instructions.
Normal Findings
Method: Spectrophotometry.
| Age | Conventional Units | SI Units (Conventional Units × 0.4114) |
|---|---|---|
| Newborn | 1.7–2.5 mg/dL | 0.7–1 mmol/L |
| Child | 1.7–2.3 mg/dL | 0.7–0.95 mmol/L |
| Adult | 1.6–2.2 mg/dL | 0.66–0.91 mmol/L |
| Pregnant female | ||
| First and second trimesters | 1.5–2.2 mg/dL | 0.63–0.91 mmol/L |
| Third trimester | 1.1–2.2 mg/dL | 0.46–0.91 mmol/L |
| Conventional Units | SI Units (Conventional Units × 0.4114) |
|---|---|
| 20–200 mg/24 hr | 8.2–82.3 mmol/24 hr |
Critical Findings and Potential Interventions
Blood: 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)
Blood: 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 confusion, convulsions, decrease in reflexes, dizziness, dysrhythmias (ventricular), hyperactivity, nausea, tetany, tremors, vomiting, and weakness 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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