Abnormal serum anion gap Elevated serum anion gap 2018-07-07T14:29:56Z Elevated values of the serum anion gap most commonly indicate metabolic acidosis but can reflect laboratory error, metabolic alkalosis, hyperphosphatemia, or paraproteinemia. Metabolic acidosis can be divided into high anion and normal anion gap varieties, which can be present alone or concurrently. An abnormally high value of the serum anion gap (the sum of serum chloride and bicarbonate concentrations subtracted from the serum sodium concentration).