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.
Blood
| Age | Conventional Units | SI Units (Conventional Units × 0.4114) |
|---|---|---|
| Newborn–2 yr | 1.6–2.7 mg/dL | 0.7–1.1 mmol/L |
| Child | 1.6–2.5 mg/dL | 0.7–1 mmol/L |
| Adult | 1.7–2.3 mg/dL | 0.7–0.95 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 |
Urine
| Conventional Units | SI Units (Conventional Units × 0.4114) | ||
|---|---|---|---|
| 51–269 mg/24 hr | 21–110.7 mmol/24 hr |
Blood
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.
(Study type: Blood collected in a gold-, red-, or red/gray-top tube; Urine from a random or timed specimen collected in a clean plastic collection container with 6N hydrochloric acid as a preservative (obtained from the testing laboratory); related body system: .)
Magnesium, the fourth-most abundant cation and the second-most abundant intracellular cation, is required as a cofactor in numerous crucial enzymatic processes, such as protein synthesis, muscle contraction, nucleic acid synthesis, oxidative phosphorylation, and glycolysis. Magnesium is also required for the use of adenosine diphosphate as a source of energy; almost every enzymatic reaction that uses phosphorus as an energy source must first be activated by magnesium. Magnesium is needed for the transmission of nerve impulses, maintenance of cell membranes, normal cardiac function, muscle contraction/relaxation, and blood clotting. It helps in the regulation of parathyroid hormone levels (similar to calcium), blood pressure, and insulin metabolism (blood glucose management); absorption of sodium, potassium, calcium, and phosphorus; utilization of carbohydrate, lipid, and protein; and activation of enzyme systems that enable the B vitamins to function.
Magnesium is available in many foods, is readily absorbed by the intestines, and is distributed and stored throughout the body; only 1% of the absorbed magnesium remains in circulation. Approximately 60% of the body’s magnesium is stored in bones, the rest is deposited in muscle, soft tissue, and the liver. Together, the minerals calcium, magnesium, and phosphorus account for 98% of the body’s mineral content; maintenance of their concentrations are interrelated. The metabolic functions of calcium and magnesium are similar, and the processes of absorption (intestinal) and excretion (renal) are interdependent; dietary intakes of calcium and magnesium inversely affect the absorption of the other, high calcium intake may decrease magnesium absorption, while low magnesium intake may increase calcium absorption. Magnesium deficiency severe enough to cause hypocalcemia and cardiac dysrhythmias can exist despite normal serum magnesium levels. Note: Calcium and phosphorus are also interrelated with respect to absorption and metabolic function. They have an inverse relationship with respect to concentration; serum phosphorus is increased when serum calcium is decreased. Electrolyte balance is a complicated and dynamic series of interrelated feedback systems often involving organ-specific hormones.
The increased nutritional demands of a developing fetus during pregnancy are often associated with corresponding maternal deficiencies, including a lower than normal magnesium level. Magnesium supplementation during pregnancy may be ordered in the form of oral prenatal vitamins, intermittent intramuscular injections, or IV administration depending on the degree of deficiency. Magnesium can be used to inhibit preterm labor by lowering calcium in uterine cells, causing the uterine muscles to relax. Magnesium is also used to help prevent and treat pre-eclampsia and eclampsia.
Regulating electrolyte balance is one of the major functions of the kidneys. In normally functioning kidneys, urine levels increase when serum levels are high and decrease when serum levels are low to maintain homeostasis. Urine magnesium levels reflect magnesium deficiency before serum levels. Analyzing these urinary levels can provide important clues as to the functioning of the kidneys and other major organs. Tests for electrolytes, such as magnesium, in urine usually involve timed urine collections over a 12- or 24-hr period. Measurement of random specimens may also be requested.
Summary of significant electrolytes/minerals (Note: Bicarbonate HCO3- is not a mineral)
| Intracellular | Extracellular | ||
| Cation (+) Positive | Anion (-) Negative | Cation (+) Positive | Anion (-) Negative |
| K+ Potassium is the major intracellular cation | PO43-Phosphate is the major intracellular anion | Na+ Sodium is the major extracellular cation | Cl- Chloride is the major extracellular anion |
| Mg2+ (Magnesium) | Ca2+ (Calcium) | HCO3- Bicarbonate is the second most important extracellular anion | |
Blood
Urine
Blood
Urine
Other Considerations
Increased In
Blood
Urine
Decreased In
Blood
Urine
Potential Problems: Assessment & Nursing Diagnosis/Analysis
| Problems | Signs and Symptoms | ||
|---|---|---|---|
| Electrolytes (decreased magnesium related to metabolic imbalance, increased renal secretion, decreased intestinal absorption, intestinal loss secondary to nasogastric tube suction, diarrhea, malabsorption, laxative abuse, chronic alcohol use) | Deficit Nystagmus, fatigue, convulsions, weakness, numbness, tetany, spasms, tremors, mood changes, irritability, hallucinations, confusion, depression, psychosis, muscle weakness, unsteady gait, hypotension, tachycardia, Chvostek or Trousseau signs | ||
| Electrolytes (increased magnesium related to metabolic imbalance, renal failure in conjunction with increased magnesium consumption, obstetric patients treated with magnesium, adrenocortical insufficiency, hypothermia, shock) | Excess Nausea, vomiting, diarrhea, diaphoresis, flushing, sensation of heat, decreased mental functioning, disorientation, confusion, weakness, paralysis, fatigue, drowsiness, hypotension, bradycardia, tachycardia, respiratory depression, coma |
Before the Study: Planning and Implementation
Teaching the Patient What to Expect
Potential Nursing Actions
After the Study: Implementation & Evaluation Potential Nursing Actions
Treatment Considerations
Electrolytes: Deficient Magnesium
Electrolytes: Excess Magnesium
Avoiding Complications
Nutritional Considerations
Safety Considerations
Clinical Judgement
Follow-Up Evaluation and Desired Outcomes