🧲 Fractional Excretion of Magnesium (FEMg)
UseWhen to use: hypomagnesemia workup with paired urine/plasma Mg and creatinine.
Strata<2% extrarenal cue; >4% renal wasting cue (teaching bands).
LimitsWhen not to use: during IV Mg infusion without timing care. · Pitfall: mismatched units. · Diuretics raise FEMg.
SourceStandard FEMg teaching formula
This-shift next steps
After scoring: open the scene pack, peer scores, and the matching pathway. Local reference — no HIS write.
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Methodology · worked example, guidelines & full notes
Paired Mg/Cr.
When to use
When to use: hypomagnesemia workup with paired urine/plasma Mg and creatinine.
How it works
FEMg%=(UMg×PCr)/(PMg×UCr)×100.
Key points
- Paired Mg/Cr.
- <2% vs >4%.
- Next: meds / GI review.
References
- Standard FEMg teaching formula
Worked calculation
The values below come from this tool's own example placeholders and are computed server-side with the formula shown on this page, so the arithmetic can be checked quickly. It demonstrates how to substitute values only — it is not clinical advice and not a real case.
| Urine Mg | 5 mg/dL |
|---|---|
| Plasma Mg | 1.5 mg/dL |
| Urine creatinine | 80 mg/dL |
| Plasma creatinine | 1.0 mg/dL |
→FEMg4.2%
- Cue：>4% — favors renal Mg wasting
- ÷0.7 teaching：6.0%
Verification & sources · governance
FAQ
Frequently asked questions
- Does Fractional Excretion of Magnesium (FEMg) upload patient data? Where is it calculated?
- Calculation runs locally in the browser; inputs and results are not uploaded. For licensed clinicians only; interpret with history, investigations and local protocols — not a diagnosis or prescription.
- How is Fractional Excretion of Magnesium (FEMg) calculated in practice? Can you show a worked example?
- Inputs: Urine Mg 5 mg/dL, Plasma Mg 1.5 mg/dL, Urine creatinine 80 mg/dL, Plasma creatinine 1.0 mg/dL → Result: FEMg 4.2 %（Cue: >4% — favors renal Mg wasting, ÷0.7 teaching: 6.0%）