Not medically reviewed
Blood gases
Base excess (BE)
Not medically reviewed · Content last updated · 1 min read ·
This is the date the draft was written, not a medical review date.
A calculated estimate of the amount of strong acid or base needed to restore blood to pH 7.40 at a PaCO2 of 40 mmHg. It isolates the metabolic component, independently of the respiratory component.
Reference interval
| Conventional (mEq/L) | SI (mmol/L) | |
|---|---|---|
| Adults | -2–2 mEq/L | -2–2 mmol/L |
Specimen: Arterial whole blood (calculated) · Conventional × 1 = SI
Causes of high values
Positive base excess indicates metabolic alkalosis (vomiting, diuretics, alkali administration) or renal compensation for chronic hypercapnia.
Causes of low values
A negative value (base deficit) indicates metabolic acidosis (lactic acidosis, ketoacidosis, renal failure, diarrhoea, hyperchloraemic acidosis) or compensation for chronic respiratory alkalosis. Large deficits in trauma suggest shock and ongoing hypoperfusion.
Pre-analytical and method notes
The usual interval is -2 to +2 mmol/L. It is a derived value whose calculation (blood or standard base excess) differs between analysers, and it should be interpreted together with pH, PaCO2 and lactate. Reference intervals vary by laboratory, method and population; use the interval printed on the report.
References
- Rifai N, Horvath AR, Wittwer CT. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Elsevier, 6th edition (2018) — Tier 3 (textbook)
- Loscalzo J, et al.. Harrison's Principles of Internal Medicine. McGraw-Hill, 21st edition (2022) — Tier 3 (textbook)
- Hall JE, Hall ME. Guyton and Hall Textbook of Medical Physiology. Elsevier, 14th edition (2020) — Tier 3 (textbook)
References are listed only where the article cites them. See the sources page for the full policy. How sources are chosen and credited