Anion Gap Calculator

Table of contents:
This anion gap calculator can be used to estimate the anion gap in blood serum, measured in the levels of sodium, chloride, and bicarbonate.

In the advanced mode, you can also input the level of potassium and albumin in blood serum levels, which may sometimes allow correction in the anion gap when taking albumin into account.

Note that this is not the calculator for anion levels in urine; there is a separate calculator for that. This is just the one to use for phlebotomy.

What is an anion?

This word applies to molecular physics. There's actually two kinds of ions to concern ourselves with: cations and anions. 

An ion is any atomic unit having a new electrical charge due to an unequal number of protons and electrons. Anions (from the Greek word for "up") have a negative electrical charge, having more electrons than protons. Cations (from the Greek word for "down") have a positive charge, being exactly the opposite.

What is an anion gap?

This is the difference between the anions and cations in the blood serum. They should be equal, so the net charge is neutral. 

The usage is in diagnosing the cause of acidosis, which is highly acidic blood plasma. This typically occurs when arterial PH balances are too low. Its complement, alkalemia, occurs at abnormally high PH levels. Acidosis is a condition which presents in several conditions, such as kidney failure, poor oxygen circulation, side effects of diabetes, elevated iron levels in the blood, or methanol poisoning.

The anion gap is calculated by measuring the relative levels of concentration of anions and cations, obtained from several individual lab tests. Essentially, this is a diagnostic tool used in narrowing down a diagnosis; similar to taking a patient's temperature or measuring their blood pressure, analyzing blood plasma for anion gap can indicate a range of problems one should look for.


Each different medical lab has different formulas they use to determine the normal range, so be sure to check for the laboratory protocol wherever you're working. Special care must be taken in testing the blood sample, to ensure it is processed immediately after being collected. Keep in mind that some people can present a mildly imbalanced anion profile without having anything wrong.

The two formulas are:

Anion Gap = Sodium - (Chloride + Bicarbonate)

Or when using potassium too in advanced mode:

Anion Gap = (Sodium + Potassium) - (Chloride + Bicarbonate)

Diagnosing and treating conditions indicated by an anion gap should only be done by licensed medical professionals.

Anion Gap Calculator

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