Calculate albumin-corrected serum magnesium levels. Assess hypomagnesemia severity, estimate magnesium deficit, and review dietary sources.
The Corrected Magnesium Calculator adjusts measured serum magnesium levels for albumin concentration, providing a more accurate assessment of true magnesium status. Since approximately 25–30% of serum magnesium is bound to albumin, hypoalbuminemia (common in hospitalized, malnourished, or critically ill patients) can cause measured magnesium to appear falsely normal even when ionized (free) magnesium is dangerously low.
Hypomagnesemia affects 10–20% of hospitalized patients and up to 65% of ICU patients. It is frequently underdiagnosed because only 1% of total body magnesium resides in the blood — the rest is in bones and soft tissues. Symptoms include muscle cramps, tremors, cardiac arrhythmias (including torsades de pointes), seizures, and refractory hypokalemia or hypocalcemia.
This calculator provides the corrected magnesium value, severity classification, estimated total body deficit, renal function considerations, and a dietary magnesium source reference table. Accurate magnesium assessment is critical because both hypomagnesemia and hypermagnesemia carry serious clinical consequences. Check the example with realistic values before reporting.
Measured serum magnesium can be misleadingly normal in patients with low albumin. The corrected value reveals the true magnesium status, enabling appropriate supplementation. Hypomagnesemia is a common cause of refractory hypokalemia and hypocalcemia — correcting magnesium is essential before these electrolytes will normalize. Keep these notes focused on your operational context.
Corrected Mg (mg/dL) = Measured Mg + 0.005 × (40 − Albumin in g/L) Where Albumin in g/L = Albumin in g/dL × 10 Unit Conversion: 1 mmol/L Mg = 2.43 mg/dL Normal Range: 1.7–2.2 mg/dL (0.70–0.91 mmol/L) Estimated Deficit (mEq) ≈ (1.9 − Corrected Mg) × Weight(kg) × 0.3
Result: Corrected Mg = 2.55 mg/dL — Mildly Elevated
Measured Mg is 1.8 mg/dL, albumin is 2.5 g/dL (25 g/L). Correction: 1.8 + 0.005 × (40 − 25) = 1.8 + 0.075 = 1.875. With significant hypoalbuminemia, the correction reveals a higher true Mg. The corrected value falls in the mildly elevated range.
Magnesium is the fourth most abundant cation in the body and the second most abundant intracellular cation after potassium. It is a cofactor for over 300 enzymatic reactions including ATP synthesis, DNA replication, protein synthesis, and neuromuscular function. Only 1% of total body magnesium is in the serum, making blood levels a poor indicator of total body stores.
Hypomagnesemia causes neuromuscular irritability (tremors, tetany, seizures), cardiac arrhythmias (prolonged QT, torsades de pointes, atrial and ventricular arrhythmias), and electrolyte disturbances (refractory hypokalemia and hypocalcemia). Chronic deficiency is associated with type 2 diabetes, hypertension, cardiovascular disease, osteoporosis, and migraine headaches.
Always interpret magnesium alongside potassium, calcium, and phosphate levels. In diabetic ketoacidosis, total body magnesium is depleted even if serum levels appear normal due to hemoconcentration. As DKA is treated and fluid is given, magnesium levels often drop precipitously. Proactive supplementation is essential in these settings.
About 25–30% of serum magnesium is bound to albumin. With low albumin, the measured total magnesium appears lower even if ionized (free) magnesium is adequate. Conversely, in hypoalbuminemia, a "normal" total magnesium may mask a true deficiency of free magnesium.
Common causes include chronic alcohol use, malnutrition, GI losses (diarrhea, vomiting), renal wasting (diuretics, especially loop diuretics), PPI use, diabetic ketoacidosis, pancreatitis, and certain medications (cisplatin, amphotericin B, calcineurin inhibitors). Use this as a practical reminder before finalizing the result.
IV magnesium sulfate 1–2 g over 5–60 minutes (emergent) or 4–6 g over 24 hours. For cardiac arrest with torsades de pointes, 1–2 g IV push. Always monitor for respiratory depression and hypotension during IV infusion.
Magnesium citrate and magnesium glycinate have the best bioavailability (25–30%). Magnesium oxide, while cheap, has only ~4% absorption. Magnesium taurate is preferred for cardiac patients, while magnesium L-threonate may cross the blood-brain barrier.
Yes. Hypermagnesemia (> 2.6 mg/dL) causes hypotension, bradycardia, decreased deep tendon reflexes, and at very high levels (> 7 mg/dL), respiratory depression and cardiac arrest. It typically occurs with renal failure combined with magnesium supplementation.
Ionized (free) magnesium is the physiologically active form and is theoretically more accurate, but the assay is not widely available and not well standardized. Corrected total magnesium remains the practical clinical standard.