anion gap

gap (gap) an unoccupied interval in time; an opening or hiatus.

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air-bone gap  the lag between the audiographic curves for air- and bone-conducted stimuli, as an indication of loss of bone conduction of the ear.

anion gap  the concentration of plasma anions not routinely measured by laboratory screening, accounting for the difference between the measured anions and cations.

auscultatory gap  a period in which sound is not heard in the auscultatory method of sphygmomanometry.

interocclusal gap  see under distance.

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anion gap

n.

The difference between the sum of cations and anions found in plasma or serum.

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anion gap,

the difference between the concentrations of serum or plasma cations and anions, determined by measuring the concentrations of sodium cations and chloride and bicarbonate anions. It is helpful in the diagnosis and treatment of acidosis, and it is estimated by subtracting the sum of chloride and bicarbonate concentrations in the plasma from that of sodium. It is normally about 8 to 14 mEq/L and represents the negative charges contributed to plasma by unmeasured ions or ions other than those of chloride and bicarbonate, mainly phosphate, sulfate, organic acids, and plasma proteins. Anions other than chloride and bicarbonate normally constitute about 12 mEq/L of the total anion concentration in plasma. Acidosis can develop with or without an associated anion increase. An increase in the anion gap often suggests diabetic ketoacidosis, drug poisoning, renal failure, or lactic acidosis and usually warrants further laboratory tests.

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anion gap

method used to evaluate a patient's acid-base status; based on the observation that the sum of blood cations (sodium, potassium, chloride and bicarbonate ions) usually exceeds the sum of the anions (sulfates, phosphates, proteinates, organic acid ions); the difference between the two is the anion gap. Significant departure from the normal level of difference indicates acid-base disturbance.

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anion gap

Lab medicine A mathematic approximation of the difference between unmeasured anions–PO₄–, SO₄–, proteins and organic acids, and unmeasured cations-Ca2+, Mg2+, which normally exceed unmeasured cations; the AG is the difference between the sum of the most abundant measured serum anions–Cl– and HCO₃– and serum cations–Na+ and K+; urinary AG is calculated as Na+ + K+ – Cl– and is a crude index of the levels of urinary ammonium and used to evaluate hyperchloremic metabolic acidosis Ref range 8-16 mEq/L; AG is ↑ in renal failure due to defective renal tubular acidification with an ↑ in phosphate and sulfate, starvation-related DKA due to an accumulation of acetoacetate and β-hydroxybutyrate or alcohol abuse, in disorders of amino acid metabolism and hyperglycemic nonketotic coma due to various organic acids, in lactic acidosis, overdose or poisoning—eg salicylates, methanol ethylene glycol antifreeze or paraldehyde; AG is ↓ in hypermagnesemia, GI loss of bicarbonate, in nephrotic syndrome due to a loss of albumin which is anionic at a physiological pH, after lithium ingestion, and multiple myeloma and Waldenström's macroglobinemia, due to an ↑ in cationic proteins