Magnesium Deficit Calculator
Magnesium deficit calculator estimates replacement needs for hypomagnesemia. Normal serum magnesium is 1.7 to 2.2 mg/dL, and low levels are critical to correct before potassium replacement, as hypomagnesemia causes renal potassium wasting.
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Formula
How it works: Helps estimate total body stores deficiency, although magnesium is primarily intracellular and skeletal.
Worked Example
Understanding Magnesium Deficit in Hypomagnesemia
Magnesium is the fourth most abundant cation in the body. Only about 1% is found in blood, making serum levels a poor reflection of total body stores. Replacement is guided by clinical severity and symptoms.
- Normal serum magnesium: 1.7 to 2.2 mg/dL; hypomagnesemia is below 1.7 mg/dL
- Only 1% of body magnesium is in blood; 60% is in bone and 39% is intracellular
- Must correct magnesium before potassium, as low Mg causes renal potassium wasting
- IV Magnesium Sulfate: 1 to 2 g for mild, 2 to 4 g for severe; 2 g IV push for Torsades de Pointes
- Common causes: loop/thiazide diuretics, alcoholism, chronic diarrhea, PPI use, and malnutrition
This calculator is for educational purposes only. Magnesium replacement dosing should be guided by a healthcare professional based on severity, symptoms, and renal function.
You can also calculate changes using our Potassium Deficit Calculator or Sodium Deficit Calculator.
Frequently Asked Questions
What is a normal magnesium level?
Normal serum magnesium is 1.7 to 2.2 mg/dL. Values below 1.7 indicate hypomagnesemia, while values below 1.2 mg/dL are considered severe.
How is magnesium replaced?
IV Magnesium Sulfate (1 to 4 g depending on severity) for hospitalized or symptomatic patients. Oral Magnesium Oxide (400 to 800 mg/day) for mild or chronic outpatient supplementation.
Why is magnesium important for the heart?
Magnesium stabilizes cardiac cell electrical activity. It is the first-line treatment for Torsades de Pointes (a dangerous arrhythmia) at 2 g IV push, and helps prevent other arrhythmias in critical care.
Why correct magnesium before potassium?
Hypomagnesemia causes the kidneys to waste potassium in the urine. Without correcting magnesium first, potassium replacement will be ineffective and levels will remain low.
What causes hypomagnesemia?
Common causes include loop and thiazide diuretics, chronic alcoholism, diarrhea, proton pump inhibitor (PPI) use, malnutrition, and certain chemotherapy agents.
Is this calculator a substitute for medical advice?
No. This tool is for educational purposes only. Magnesium replacement should be guided by a healthcare professional based on clinical severity and renal function.
How do I add this Magnesium Deficit Calculator to my site?
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Medical Disclaimer
This calculator is provided for informational and educational purposes only. It is not intended as a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making any decisions based on these results. Do not disregard or delay seeking medical advice because of information obtained from this tool.
AI Assistant
Ask about this calculator
I can help you understand the magnesium deficit calculator formula, interpret your results, and answer follow-up questions.
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Our AI assistant provides general estimates and advice only. Please consult a qualified healthcare professional before making any health-related decisions.
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