Acidosis

In medicine, acidosis is "pathologic condition resulting from accumulation of acid or depletion of the alkaline reserve (bicarbonate) content of the blood and body tissues, and characterized by an increase in hydrogen ion concentration (decrease in pH). (Dorland, 27th ed)."

Metabolic acidosis
"When the delta HCO3 is less than the delta AG, a mixed metabolic alkalosis and metabolic acidosis is likely to be present." Thus for each increase in the anion gap over 12 the bicarbonate should fall by the same amount.