Question

Answer

Anion Gap = Sodium - (Bicarbonate + Chloride)
Normal value=10 - 15 mEq/L

The Anion Gap reflects the concentrations of those anions that actually are present in serum but are routinely undetermined, including negative charged plasma proteins(mainly albumin), phosphates, sulfate and organic acids(e.g., lactic acid). An increase in the anion gap represents an increase in one more of these moities, usually organic acids.
No change in the anion gap, with decreases in both plasma bicarbonate concentration and serum pH, suggests a prymary loss of bicarbonate or the addition of mineral acid.
Its is very useful in the evaluation of metabolic acidosis, because metabolic acidosis may be divided into those associated with a normal anion gap and those associated with an increased anion gap as follows:

Metabolic acidosis with an increased anion gap:

1. Ketoacidosis
   
2. Lactic acid acidosis
   
3. Renal failure
   
4. Intoxicaion
   

Metabolic acidosis with a normal anion gap(hyperchloremic metabolic acidosis:

1. Renal loss of bicarbonate
   • Proximal tubular acidosis
   • Distal tubular acidosis
   • Hyperkalemic renal tubular acidosis
   • Loss of organic anions
   • Carbonic anhydrase inhibition
2. Gastrointestinal loss of bicarbonate
   • Diarrhea
   • Pancreatic fistulas
   • Uterosigmoidostomy
3. Mineral acid administration
   • Ammonium chloride
   • Arginine hydrochloride
   • Calcium chloride

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