Gapped acidosis1/5/2023 ![]() ![]() Thus normal reference values ranged from 8 to 16 mEq/L plasma when not including and from 10 to 20 mEq/L plasma when including. In the past, methods for the measurement of the anion gap consisted of colorimetry for and as well as flame photometry for and. A normal anion gap is often defined as being within the prediction interval of 3–11 mEq/L, with an average estimated at 6 mEq/L. Therefore, according to the new classification system, a high anion gap is anything above 11 mEq/L. Modern analyzers use ion-selective electrodes which give a normal anion gap as <11 mEq/L. Also, some healthy people may have values outside of the "normal" range provided by any lab. The reference range provided by the particular lab that performed the testing should always be used to interpret the results. The anion gap varies in response to changes in the concentrations of the above-mentioned serum components that contribute to the acid-base balance.ĭifferent labs use different formulae and procedures to calculate the anion gap, so the reference range (or "normal" range) from one lab isn't directly interchangeable with the range from another. Because we know that plasma is electro-neutral (uncharged), we can conclude that the anion gap calculation represents the concentration of unmeasured anions. ![]() In normal health there are more measurable cations than measurable anions in the serum therefore, the anion gap is usually positive. Commonly 'unmeasured' anions include sulfates and a number of serum proteins. Similarly, tests do often measure the anion phosphate (PO 3−Ĥ) specifically, but it isn't used to calculate that "gap," even if it is measured. Anions that are generally considered "unmeasured" include a few normally occurring serum proteins, and some pathological proteins (e.g., paraproteins found in multiple myeloma). The cations calcium (Ca 2+) and magnesium (Mg 2+) are also commonly measured, but they aren't used to calculate the anion gap. ![]() (As discussed above, potassium may or may not be used, depending on the specific lab.) These "unmeasured" ions are mostly anions, which is why the value is called the "anion gap." īy definition, only the cations sodium (Na +) and potassium (K +) and the anions chloride (Cl −) and bicarbonate (HCO −ģ) are used to calculate the anion gap. The anion gap is representative of how many ions are not accounted for by the lab measurements used in the calculation. However, routine tests do not measure all types of ions. The total number of cations (positive ions) should be equal to the total number of anions (negative ions), so that the overall electrical charge is neutral. (Bicarbonate may also be referred to as "total CO 2" or "carbon dioxide".) Uses Ĭalculating the anion gap is clinically useful because it helps in the differential diagnosis of a number of disease states. This leaves the following equation:Īnion Gap = Sodium - (Chloride + Bicarbonate) which is logically equivalent to: Anion Gap = (the most prevalent cation) minus (the sum of the most prevalent anions) Therefore, omission of potassium has become widely accepted. The anion gap is calculated by subtracting the serum concentrations of chloride and bicarbonate ( anions) from the concentrations of sodium and potassium ( cations):ģ]) = 20 mEq/L Without potassium īecause potassium concentrations are very low, they usually have little effect on the calculated gap. The concentrations are expressed in units of milliequivalents/ liter (mEq/L) or in millimoles/litre (mmol/L). It is computed with a formula that uses the results of several individual lab tests, each of which measures the concentration of a specific anion or cation. 5 Correcting the anion gap for the albumin concentration.The term "anion gap" usually implies " serum anion gap", but the urine anion gap is also a clinically useful measure. If the gap is greater than normal, then high anion gap metabolic acidosis is diagnosed. The magnitude of this difference (i.e., "gap") in the serum is calculated to identify metabolic acidosis. The anion gap is the quantity difference between cations (positively charged ions) and anions (negatively charged ions) in serum, plasma, or urine. It may be reported with the results of an electrolyte panel, which is often performed as part of a comprehensive metabolic panel. The anion gap ( AG or AGAP) is a value calculated from the results of multiple individual medical lab tests. Pathophysiology sample values BMP/ ELECTROLYTES: ( April 2010) ( Learn how and when to remove this template message) Please help improve it to make it understandable to non-experts, without removing the technical details. This article may be too technical for most readers to understand. ![]()
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