Anion gap
The anion gap is a calculated metabolic parameters, which is useful for physicians in the differential diagnosis of metabolic acidosis.
Calculation
The anion gap is calculated by subtracting the blood serum concentrations of chloride plus bicarbonate (anions) of the concentrations of sodium plus potassium (cation ):
In everyday practice, the potassium concentration is often neglected, which results in the following formula:
Application
The anion gap reflects the non- detected anions in the plasma. These anions are affected differently depending on the type of metabolic acidosis. The primary benefit of the calculation of the anion gap is to narrow down the possible causes of metabolic acidosis in a patient. For example, in a patient who has a normal anion gap, causes are excluded, which would cause an increased anion gap.
Normal values
Modern analyzers use ion-selective electrodes. In this measurement method the normal range is between 3 and 11 mmol / l An increased anion gap is present, therefore, if the calculated value above 11 mmol / l; a reduced anion is at a calculated value of less than before 3 mmol / l.
Interpretation and Causes
The anion gap can be either increased, normal or rarely also be reduced.
An increased anion gap on the one hand indicate that a loss of HCO3- is present, which is not Cl -, but balanced as normally carried by other, unmeasured anions such as ketone bodies, lactate, phosphate, and sulfate. On the other hand, it can also be caused by the abnormal proliferation of other anions ( ketone bodies, lactate, toxins below).
Loss by an increase in Cl - - In patients with metabolic acidosis and normal anion gap of HCO3 concentration is balanced, which is why this form of metabolic acidosis is also known as hyperchloremic acidosis.
Increased anion gap ( Additionsazidose )
The Bikarbonatverbrauch is offset by unmeasured anions; thus results in a larger anion gap.
- Uremia
- Lactic acidosis
- Ketoacidosis Diabetic ketoacidosis
- Alcoholism
- Malnutrition
- Poisons or drugs: ethanol
- Ethylene glycol
- Lactic acid
- Methanol
- Paraldehyde
- Acetylsalicylic acid
- Cyanide, coupled with increased venous oxygen saturation
- Iron
- Isoniazid
Normal anion gap ( hyperchloremic acidosis, Subtraktionsazidose )
Normally, the loss of HCO3- is balanced by chloride. Then a normal anion gap is present ( at elevated chloride concentration).
- Gastrointestinal loss of HCO3- ( = diarrhea) (Note: vomiting caused by the stomach acid is lost, a hypochloremic alkalosis)
- Renal loss of HCO3- ( In distal renal tubular acidosis)
- Renal dysfunction (renal failure, hypoaldosteronism, distal renal tubular acidosis)
- Ingestion of: Ammonium chloride or acetazolamide
- Hyperalimentation by liquids ( total parenteral nutrition)
- Alcohols ( particularly ethanol) can affect the anion, by inducing the alcohol dehydrogenase.
Reduced anion gap
A reduced anion gap is rare. However, they can be caused by the presence of abnormal positively charged proteins, such as multiple myeloma, or reduced serum albumin levels.
Anion in the urine
The anion gap in the urine ( urinary anion gap english, UAG) is the differentiation of hyperchloremic metabolic acidosis. In chronic metabolic acidosis, the kidney is able to acids in the urine by Ammoniumsekretion. In the calculation, however, are only measured in the urine Na -, K - and Cl - containing concentrations.
The normal range is in this case from 20 to 60 mmol / l Try the kidneys, now a extrarenal acidosis (eg diarrhea with HCO3 - loss ) compensate for the anion in the urine is negative, since the Na - and K concentrations decrease in favor of not contained in the bill NH4 cations. In a renal tubular acidosis, however, the gap remains positive.