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Pathophysiology sample values
Na+=140 Cl=100 BUN=20 /
K+=4 CO2=22 PCr=1.0 \
HCO3-=24 paCO2=40 paO2=95 pH=7.40
pACO2=36 pAO2=105 A-a g=10
Ca=9.5 PO4=1 Mg2+=2.0
CK=55 BE=−0.36 AG=16
PMO = 300 PCO=295 POG=5 BUN:Cr=20
UNa+=80 UCl=100 UAG=5 FENa=0.95
UK+=25 USG=1.01 UCr=60 UO=800
LDH=100 TP=7.6 AST=25 TBIL=0.7
ALP=71 Alb=4.0 ALT=40 BC=0.5
AST/ALT=0.6 BU=0.2
AF alb=3.0 SAAG=1.0 SOG=60
CSF alb=30 CSF glu=60 CSF/S alb=7.5 CSF/S glu=0.4

In human physiology, base excess (see: base) refers to the amount of acid required to return the blood pH of an individual to the reference interval pH (7.35–7.45) with the amount of carbon dioxide held at a standard value. The value is usually reported in units of (mEq/L). The normal reference range is somewhere between −5 to +3. Comparison of the base excess with the reference range assists in determining whether an acid/base disturbance is caused by a respiratory, metabolic, or mixed metabolic/respiratory problem.

Another definition for base excess is the amount of acid or base that must be added to a litre of blood (ECF) to return the pH to 7.4 at a pCO2 of 40 mmHg (5.3 kPa).

The term and concept were first introduced by Poul Astrup and Ole Siggaard-Andersen in 1958.



A base excess value exceeding +3 indicates that a patient has blood that requires abnormally increased amounts of acid to return the pH to neutral, thus indicating alkalosis. More simply, a BE=3 means the body has 3 equivalents more of base than acid—i.e., it has excess base, and is thus alkalotic. Whereas a value below −3 usually indicates that the patient is acidotic, ie excess acid needs to be removed from the blood to return the pH back to normal.

Examples of common situations where you would see a base excess less than −3 would include lactic acidosis (for example after anaerobic metabolism during heavy exercise) and diabetic ketoacidosis. A common example of a situation associated with a base excess exceeding +3 is in persistent vomiting causing loss of acidic gastric fluids.


It can be estimated by the equation:[1]  Base~excess = 0.93 \times \left ( \left [ HCO_3 \right ] - 24.4 + 14.8 \times \left ( pH - 7.4 \right ) \right ), where [HCO3] denotes the serum bicarbonate concentration.

Alternatively expressed as  Base~excess = 0.93 \times [HCO_3] + 13.77 \times pH - 124.58

Actual and standard

Actual base excess is the base excess in the blood.

Standard base excess is the value of base excess when the hemoglobin value is 5 g/dl. This gives a better view of the base excess of the entire extracellular fluid.[2]

See also


  1. ^ Medical Calculators > Calculated Bicarbonate & Base Excess Steven Pon, MD, Weill Medical College of Cornell University
  2. ^ Acid-Base Tutorial — Terminology

External links



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