REFERENCE INTERVAL:
12 - 20 mmol/L
Corrected Anion Gap = Anion Gap + [0.25 x (40 - albumin)]
DIAGNOSTIC USE:
The anion gap is a mathematical calculation of the difference between the measured cations and anions, as shown in the above equation.
The concentration of the measured cations exceeds the concentration of the measured anions, and this difference is referred to as the "anion" gap. The normal anion gap is due to the presence of unmeasured anions, mainly plasma albumin. The corrected anion gap should be calculated and used if the plasma albumin concentration is low.
The total concentration of anions and cations in serum is always equal. If the concentration of a cation or anion changes, electrochemical neutrality is maintained by changing the balance of other ions. For example, an increase in unmeasured anions will usually result in a decrease in measured anions, and so the anion gap will increase.
The anion gap is useful for distinguishing the cause of metabolic acidosis.
The anion gap is increased in metabolic acidosis due to ketones, lactate, and other organic acids. The anion gap is normal in renal tubular acidosis and in acidosis due to bicarbonate loss (e.g. diarrhoea).
The gap is increased in poisoning by ethylene glycol, paraldehyde, methanol, and salicylate. A number of other drugs have secondary effects on anion gap.
The anion gap may be decreased in dilutional states, with some paraproteins, hypoalbuminaemia, and where there is a marked increase in unmeasured cations: lithium, magnesium, calcium, etc.)
| ANION GAP - Calculation {For this calculation to be done you must test for Electrolytes + Chloride + Bicarbonate - Heparin or Plain.} |
Reference:Hatherill et al. Correction of the anion gap for albumin. Arch Dis Child. 2002; 87:526
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