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High anion gap metabolic acidosis is a form of metabolic acidosis characterized by a high anion gap (a medical value based on the concentrations of ions in a patient's serum). Metabolic acidosis occurs when the body produces too much acid , or when the kidneys are not removing enough acid from the body.
The anion gap is the quantity difference between cations (positively charged ions) and anions (negatively charged ions) in serum, plasma, or urine. The magnitude of this difference (i.e., "gap") in the serum is calculated to identify metabolic acidosis. If the gap is greater than normal, then high anion gap metabolic acidosis is diagnosed.
In general, the cause of a hyperchloremic metabolic acidosis is a loss of base, either a gastrointestinal loss or a renal loss [citation needed]. Gastrointestinal loss of bicarbonate (HCO − 3) [citation needed] Severe diarrhea (vomiting will tend to cause hypochloraemic alkalosis) Pancreatic fistula with loss of bicarbonate rich pancreatic fluid
Elevated protein (albumin, globulins) may theoretically increase the anion gap but high levels are not usually encountered clinically. Hypoalbuminaemia, which is frequently encountered clinically, will mask an anion gap. As a rule of thumb, a decrease in serum albumin by 1 G/L will decrease the anion gap by 0.25 mmol/L [citation needed]
The serum anion gap is useful for determining whether a base deficit is caused by addition of acid or loss of bicarbonate. Base deficit with elevated anion gap indicates addition of acid (e.g., ketoacidosis). Base deficit with normal anion gap indicates loss of bicarbonate (e.g., diarrhea).
An elevated anion gap metabolic acidosis and ketosis is the classic present. [3] However, a mixed acid-base disorder may be present especially if vomiting is contributing to a hypochloremic alkalosis. [2] The ketone which is present is mostly beta-hydroxybutyrate rather than acetoacetate resulting in only a weakly positive nitroprusside test. [2]
An anion-gap metabolic acidosis occurs later in the course of the overdose, especially if it is a moderate to severe overdose, due to the increase in protons (acidic contents) in the blood. The diagnosis of poisoning usually involves measurement of plasma salicylate, the active metabolite of aspirin, by automated spectrophotometric methods.
When this happens the numerator is large, the denominator is small, and the result is a delta ratio which is high (>2). This means a combined high anion gap metabolic acidosis and a pre-existing either respiratory acidosis or metabolic alkalosis (causing the high bicarbonate) – i.e. a mixed acid–base metabolic acidosis. [citation needed]