Anion gap - plasma or serum
Last updated: Wednesday, 07, April, 2004
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| Item | Process |
|---|---|
| Specimen | 5 mL blood in lithium heparin or plain tube. |
| Method | Calculated parameter: Anion gap = (Na + K) - (Cl + HCO3). Some laboratories do not include K in the equation. |
| Reference Interval | 8-16 mmol/L (4-13 mmol/L if K not included). |
| Application | Investigation of aetiology of metabolic acidosis. |
| Interpretation | An increased anion gap is seen in metabolic acidosis due to unmeasured anions that accumulate in renal failure; ketoacidosis; lactic acidosis; drug (eg, salicylate), ethylene, glycol and methanol toxicity; and in any situation where increased accumulation of acidic anions occurs. Metabolic acidosis with a normal anion gap is seen in renal tubular acidosis and in other causes of bicarbonate loss eg, diarrhoea. |
| Reference | Sirker AA et al. Anaesthesia 2002; 57(4): 348-356. |