Base Excess – Definition, Normal Values and Significance
Base excess is a laboratory value from blood gas analysis that evaluates the acid-base balance. It indicates whether there is a surplus or deficit of buffer bases in the blood.
Things worth knowing about "Base Excess"
Base excess is a laboratory value from blood gas analysis that evaluates the acid-base balance. It indicates whether there is a surplus or deficit of buffer bases in the blood.
What Is Base Excess?
Base excess (abbreviated as BE) is a key parameter in blood gas analysis (BGA). It describes the amount of acid or base required to bring 1 litre of blood to a pH of 7.4 at a standardised carbon dioxide partial pressure (pCO2 of 40 mmHg) and a body temperature of 37 °C. Base excess provides information about whether a metabolic imbalance in the acid-base balance is present.
Normal Values
The reference range for base excess in healthy adults is between -2 and +2 mmol/l. Values outside this range indicate a disturbance in the acid-base equilibrium:
- Positive base excess (BE > +2 mmol/l): Indicates metabolic alkalosis (too many bases or too few acids in the blood).
- Negative base excess (BE < -2 mmol/l): Indicates metabolic acidosis (too many acids or too few bases in the blood). A strongly negative value is also referred to as a base deficit.
Causes of an Altered Base Excess
Elevated Base Excess (Metabolic Alkalosis)
- Vomiting with loss of gastric acid
- Excessive intake of antacids or sodium bicarbonate
- Diuretic therapy with potassium loss
- Hyperaldosteronism (increased aldosterone production)
Reduced Base Excess / Base Deficit (Metabolic Acidosis)
- Diabetic ketoacidosis (metabolic decompensation in diabetes mellitus)
- Lactic acidosis (accumulation of lactic acid, e.g. in shock states)
- Renal failure with reduced acid excretion
- Severe diarrhoea with loss of bicarbonate
- Poisoning (e.g. with salicylates or methanol)
Clinical Significance
Base excess is primarily used in intensive care medicine, anaesthesiology, and emergency medicine to assess the severity of a metabolic disorder. It helps distinguish metabolic from respiratory (breathing-related) acid-base disturbances. A strongly negative base deficit can indicate a shock state or severe tissue hypoperfusion and requires immediate medical intervention.
In addition to base excess, blood gas analysis also measures other parameters such as pH, pCO2, pO2, and bicarbonate (HCO3-) to provide a complete picture of the acid-base status.
Measurement of Base Excess
Base excess is measured as part of an arterial or venous blood gas analysis. A small blood sample is taken and evaluated using a blood gas analyser. The measurement takes only a few minutes and quickly provides important information about the metabolic status of the patient.
References
- Kellum JA et al. - Disorders of Acid-Base Balance. In: Critical Care Medicine. Elsevier, 2018.
- Berend K, de Vries APJ, Gans ROB - Physiological Approach to Assessment of Acid-Base Disturbances. New England Journal of Medicine, 2014; 371:1434-1445.
- World Health Organization (WHO) - The Clinical Use of Blood in Medicine, Obstetrics, Paediatrics, Surgery and Anaesthesia, Trauma and Burns. WHO Press, Geneva, 2001.
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