Nephrology Book


Fractional Excretion of Bicarbonate

Aka: Fractional Excretion of Bicarbonate, FE-HCO3
  1. Indications
    1. Differentiate Proximal RTA from Distal RTA
    2. Requires that serum bicarbonate be normal
  2. Calculation
    1. FE-HCO3 = (uHCO3 x sCr) / (sHCO3 x uCr)
    2. Annotation
      1. Where FE-HCO3 is Fractional Excretion of Bicarbonate
      2. Where uHCO3 is urine bicarbonate
      3. Where sHCO3 is serum bicarbonate
      4. Where uCr is Urine Creatinine
      5. Where sCr is Serum Creatinine
  3. Interpretation
    1. FE-HCO3 <5%: Distal RTA
    2. FE-HCO3 >15%: Proximal RTA
      1. Assumes serum bicarbonate >20 meq/L

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