FERE: Fractional excretion of random electrolytes

Magnesium:

• 142 controls: 1.8% (range 0.5-4%)
• 74 hypomagnesemic
• Extra-Renal origin 1.4% (range 0.5-2.7%)
• Renal origin 15% (range 4-48%)
• Authors conclusion: >4% per cent is indicative of inappropriate renal magnesium loss

Fractional excretion of magnesium in normal subjects and in patients with hypomagnesemia.

Potassium

• 312 normal subjects: 8% (range 4-16%)
• 84 hypokalaemic patients
• Extra-renal origin: 2.8% (range 1.5-6.4%)
• Renal origin: 15% (range 9.5-24%)
• Authors conclusion: >6.5% per cent is indicative of inappropriate renal potassium loss

Fractional excretion of potassium in normal subjects and in patients with hypokalaemia.