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