Corrected Magnesium Calculator

Corrected Mg²⁺ = Measured Mg²⁺ + 0.02 × (4.0 − Albumin)

Low albumin masks true magnesium status. This calculator adjusts serum magnesium for albumin to detect hidden hypomagnesemia — critical for managing refractory hypokalemia and hypocalcemia.

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Interactive Tool

Calculate Your Corrected Magnesium

Enter serum magnesium and albumin to get the corrected value with clinical interpretation.

Lab Values

Magnesium in mg/dL, Albumin in g/dL

Results

Enter values and click Calculate to see your results

Formula & Calculation

Corrected Magnesium Formula

How to adjust magnesium when albumin is abnormal.

Standard Correction

Corrected Mg = Mg + 0.02 × (4.0 − Albumin g/dL)

For every 1 g/dL drop in albumin below 4.0, add 0.02 mg/dL to the measured magnesium. The correction is smaller than calcium because less magnesium is protein-bound.

Why Correct?

~33% of Mg²⁺ is albumin-bound

Unlike calcium (45% bound), only about 33% of serum magnesium is protein-bound. The remaining is ionized (55%) or complexed (12%). The correction is smaller but still clinically important in severely hypoalbuminemic patients.

Step-by-Step Calculation

1
Measure serum magnesium. For example: 1.8 mg/dL.
2
Check albumin. Normal is 4.0 g/dL. If patient albumin is 2.0 g/dL, deficit = 2.0 g/dL.
3
Apply correction. 0.02 × (4.0 − 2.0) = 0.04 mg/dL.
4
Add to measured Mg. Corrected Mg = 1.8 + 0.04 = 1.84 mg/dL — still within normal range.

Live Calculation Preview

Updates in real-time as you change values above.

Understanding the Basics

What is Corrected Magnesium?

Why magnesium correction matters clinically.

Magnesium Distribution

Serum magnesium exists in three fractions: ~55% ionized (free), ~33% protein-bound (mostly albumin), and ~12% complexed with anions like citrate, phosphate, and oxalate. Only ionized magnesium is physiologically active.

The Hidden Deficiency

Magnesium deficiency is one of the most underdiagnosed electrolyte disorders. Serum Mg²⁺ reflects only 1% of total body magnesium (99% is intracellular or in bone). A "normal" serum level doesn't rule out deficiency. The correction for albumin adds another layer of accuracy but intracellular assessment remains challenging.

Ionized Mg²⁺ (55%)
Protein-Bound (33%)
Complexed (12%)
Reference Values

Corrected Magnesium Normal Range

Reference ranges for serum magnesium.

ParameterNormal RangeUnitNotes
Serum Mg²⁺1.7 – 2.3mg/dLWith normal albumin
Ionized Mg²⁺0.44 – 0.59mmol/LDirect measurement (limited availability)
Albumin3.5 – 5.0g/dLPrimary Mg-binding protein
Corrected Mg²⁺1.7 – 2.3mg/dLAfter albumin adjustment

Where Does Your Corrected Mg²⁺ Fall?

This gauge shows your corrected magnesium level.

Clinical Interpretation

Corrected Magnesium Interpretation

What different corrected magnesium values mean clinically.

🔴

Hypermagnesemia

Corrected Mg > 2.3 mg/dL
  • Usually iatrogenic (Mg infusions)
  • Renal failure (impaired excretion)
  • Hyporeflexia → respiratory depression
  • Cardiac conduction delays
  • Stop Mg supplementation immediately
🟢

Normal Magnesium

Corrected Mg 1.7–2.3 mg/dL
  • Normal Mg homeostasis
  • Adequate for enzyme function
  • Does not rule out intracellular depletion
  • Monitor in at-risk patients
  • Consider 24h urine Mg if clinically suspicious
🔵

Hypomagnesemia

Corrected Mg < 1.7 mg/dL
  • GI losses (diarrhea, malabsorption)
  • Diuretics (loop and thiazide)
  • Alcoholism
  • PPI use (long-term)
  • Causes refractory hypoK⁺ and hypoCa²⁺
When to Use

When to Correct and Supplement Magnesium

Clinical scenarios where magnesium management is critical.

Key Indications

  • Refractory hypokalemia — If K⁺ won't correct despite replacement, check and correct Mg²⁺ first. Mg is essential for the Na-K-ATPase pump.
  • Refractory hypocalcemia — Mg is needed for PTH secretion and end-organ response. Correct Mg before Ca.
  • Cardiac arrhythmias — Hypomagnesemia predisposes to torsades de pointes, atrial fibrillation, and digoxin toxicity.
  • ICU patients — Critically ill patients with low albumin may have masked hypomagnesemia.
  • Chronic diuretic use — Both loop and thiazide diuretics cause renal Mg wasting.
Common Questions

Frequently Asked Questions

Answers to common questions about corrected magnesium.

About 33% of serum magnesium is bound to albumin. When albumin is low, total Mg²⁺ drops even if the active ionized fraction is normal. The correction adjusts for this binding to provide a more accurate estimate of magnesium status, though the effect is smaller than for calcium.
Symptoms include neuromuscular (tremor, tetany, muscle cramps, seizures), cardiac (arrhythmias, QT prolongation, torsades de pointes), and metabolic (refractory hypokalemia and hypocalcemia). Severe hypomagnesemia (<1.0 mg/dL) can be life-threatening.
Magnesium is essential for PTH secretion and action — hypomagnesemia causes functional hypoparathyroidism and refractory hypocalcemia. Mg also maintains the Na-K-ATPase pump in the kidney — when Mg is low, the pump fails, causing renal potassium wasting and refractory hypokalemia. Always check Mg when K⁺ or Ca²⁺ won't correct.
Supplement when corrected Mg²⁺ is below 1.7 mg/dL, or when clinically indicated (arrhythmias, refractory hypokalemia/hypocalcemia). IV magnesium sulfate is preferred for severe or symptomatic cases. Oral magnesium oxide or citrate can be used for chronic repletion. Remember: serum Mg reflects only 1% of total body stores.
Major causes include GI losses (diarrhea, vomiting, malabsorption), renal losses (loop/thiazide diuretics, aminoglycosides, cisplatin, amphotericin B), alcoholism (both poor intake and renal wasting), and proton pump inhibitors (long-term use impairs intestinal absorption). Diabetic ketoacidosis also causes significant Mg losses.
The correction formula provides a reasonable estimate but has limitations. The correction factor is small (0.02 per g/dL albumin deficit), so the impact is modest compared to calcium correction. For accurate assessment, ionized magnesium measurement is preferred when available, though it's not widely offered. Clinical context and 24-hour urine magnesium excretion often provide more useful information.