Fractional Excretion of Bicarbonate (FEHCO3)
Fractional excretion of bicarbonate: (urine HCO₃ / plasma HCO₃) × (plasma Cr / urine Cr) × 100; > 15% suggests proximal (type II) RTA while < 5% is consistent with distal (type I) RTA or normal.
Open the calculator → Runs in your browser. Data leaves only if you deliberately send a problem report from the interactive tool.
Example
- Urine bicarbonate
- 20 mEq/L
- Plasma bicarbonate
- 24 mEq/L
- Plasma creatinine
- 1.0 mg/dL
- Urine creatinine
- 50 mg/dL
Result: Fractional excretion of bicarbonate 1.67% — suggests distal (type I) RTA or normal (< 5%).
The tool opens with these values already filled in. Replace them with your own.
What the result means
- < 5%
- Suggests distal (type I) RTA or normal handling.
- > 15%
- Suggests proximal (type II) RTA. Measured after bicarbonate loading. A diagnostic ratio, not a treatment order.
What you enter
- Urine bicarbonate
- Plasma bicarbonate
- Plasma creatinine
- Urine creatinine
How this is calculated
Kurtzman NA. Renal tubular acidosis syndromes. South Med J. 2000;93(11):1042-1052. Cutoffs: Palmer BF, Kelepouris E, Clegg DJ. Renal tubular acidosis: core curriculum 2025. Am J Kidney Dis. Read the source ↗
A reference and educational tool. Not medical, legal, or financial advice, and not a substitute for clinician judgment.