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Renal

Fractional Excretion of Magnesium (FEMg)

Fraction of filtered magnesium excreted in urine — distinguishes renal magnesium wasting from extrarenal loss in hypomagnesaemia.

Written for clinicians. If you're a parent or patient, don't act on these numbers — talk to your child's doctor.

Inputs

FieldUnitNotes
Urine magnesium mg/dL 0–100
Plasma magnesium mg/dL 0.5–6
Urine creatinine mg/dL 1–1000
Plasma creatinine mg/dL 0.1–30

FAQ

What is the Fractional Excretion of Magnesium (FEMg)?

Fraction of filtered magnesium excreted in urine — distinguishes renal magnesium wasting from extrarenal loss in hypomagnesaemia.

What inputs does the Fractional Excretion of Magnesium (FEMg) need?

Urine magnesium (mg/dL), Plasma magnesium (mg/dL), Urine creatinine (mg/dL), Plasma creatinine (mg/dL).

Related guides

Fractional Excretion of Magnesium (FEMg): Distinguishing Renal Wasting from GI Loss

FEMg quantifies the fraction of filtered magnesium excreted in urine — the 0.7 protein-binding correction, the >2–4% renal-wasting cutoff in hypomagnesaemia, and why timing matters.

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