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Adjusts measured serum magnesium for hypoalbuminemia. When serum albumin is low, measured total magnesium is falsely reduced because less magnesium is bound to proteins. This correction estimates the physiologically relevant magnesium level.
Corrected Mg (mmol/L) = Measured Mg (mmol/L) + 0.005 × (40 − Albumin in g/L)
0.75–1.05 mmol/L
Approximately 25–30% of serum magnesium binds to albumin. When albumin falls, measured total magnesium decreases proportionally even though ionized (biologically active) magnesium may remain normal. The Kroll-Elin correction normalizes the measured value to a reference albumin of 40 g/L. This is analogous to the well-established corrected calcium formula but uses a different coefficient reflecting magnesium's lower protein-binding fraction.
Specialty
Internal MedicineCategory
LaboratoryDifficulty
Basic
Estimated Time
30 seconds
Version
1.0
Last Updated
2026-08
Formula
Keywords
Normal Range
0.75–1.05 mmol/L
| Classification | Range |
|---|---|
Severe hypomagnesemia | <0.50 mmol/L |
Moderate hypomagnesemia | 0.50–0.65 mmol/L |
Mild hypomagnesemia | 0.66–0.74 mmol/L |
Normal magnesium | 0.75–1.05 mmol/L |
Mild hypermagnesemia | 1.06–1.50 mmol/L |
Moderate hypermagnesemia | 1.51–2.00 mmol/L |
Severe hypermagnesemia | >2.00 mmol/L |
Adjusts measured serum magnesium for hypoalbuminemia. When serum albumin is low, measured total magnesium is falsely reduced because less magnesium is bound to proteins.
A corrected magnesium below 0.75 mmol/L suggests true hypomagnesemia. A value above 1.05 mmol/L suggests hypermagnesemia. The correction is most useful when albumin is significantly reduced (e.g., critical illness, liver disease, nephrotic syndrome).
Approximately 25–30% of serum magnesium binds to albumin. When albumin falls, measured total magnesium decreases proportionally even though ionized (biologically active) magnesium may remain normal. This correction is analogous to the corrected calcium formula.
A patient with liver cirrhosis has a measured magnesium of 0.7 mmol/L and albumin of 20 g/L.
Inputs:
Corrected Mg = 0.7 + 0.005 × (40 − 20) = 0.7 + 0.1 = 0.8 mmol/L — within normal range, suggesting the measured value was falsely low due to hypoalbuminemia.
About 25–30% of serum magnesium is bound to albumin. When albumin is low (hypoalbuminemia), measured total magnesium appears falsely low even though ionized magnesium may be normal. The correction estimates what total magnesium would be at a normal albumin of 40 g/L.
A corrected magnesium below 0.75 mmol/L suggests true hypomagnesemia. Common causes include gastrointestinal losses (vomiting, diarrhea), renal wasting (diuretics), malnutrition, alcohol use disorder, and critical illness. Hypomagnesemia can cause cardiac arrhythmias, seizures, and refractory hypokalemia.
Yes. Ionized (free) magnesium directly measures the biologically active fraction and is not affected by albumin. However, ionized magnesium assays require specialized analyzers that are not available in all clinical settings. The corrected magnesium is a practical alternative.
Both correct for albumin-binding effects, but they use different coefficients. Calcium uses 0.8 (g/dL units) because ~40–50% of calcium binds to albumin. Magnesium uses 0.005 (g/L units) because only ~25–30% binds to albumin. They are distinct analytes with distinct clinical implications.
Avoid using this correction in neonates (different binding dynamics), when ionized magnesium testing is available and reliable, or when acid-base disturbances or hyperphosphatemia are present (these alter magnesium binding independently of albumin).
Disclaimer: This calculator is intended for educational and clinical decision support. The corrected magnesium is an estimate; direct ionized magnesium measurement is the gold standard when available.
Interpreting magnesium in hypoalbuminemic patients.
Does not replace ionized magnesium measurement.
Correcting total calcium for hypoalbuminemia.
Different analyte; does not assess magnesium status.
Screening for high anion gap metabolic acidosis.
Does not directly assess magnesium.