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

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