: Anion Gap, Serum or Plasma, Calculated, Substance Concentration

: What Is the Anion Gap?

: The anion gap is not measured directly. It is calculated from substances your blood test already reports, typically sodium, chloride, and bicarbonate (or total CO2). Because positively and negatively charged particles in the body must balance, this calculation gives an estimate of the unmeasured negatively charged particles, or anions, in your blood.

: Why Is It Ordered?

: Your clinician may include an anion gap as part of an electrolyte panel or a metabolic workup. It is often used when there are signs or lab findings of an acid-base disturbance, such as unexplained changes in bicarbonate, and it can help narrow down possible causes and guide further testing.

: How the Calculation Works

: In the most common form, the anion gap is estimated by taking the sodium concentration and subtracting the chloride and bicarbonate concentrations. Some laboratories use a slightly different formula or include potassium. Because the exact formula and units can vary, the result should be interpreted using the reference information provided by the performing laboratory.

: What the Result Can Suggest

: A higher-than-expected anion gap can occur when acids build up in the blood from certain conditions, while a lower-than-expected gap may relate to other electrolyte or protein patterns. The number alone is not a diagnosis; it is interpreted together with your symptoms, other electrolyte results, kidney function, and clinical context.