1, anion gap (AG) is an index for evaluating acid-base balance, which can reflect unmeasured anion concentration in blood, such as lactic acid and ketone bodies.

2. Na+ represents the concentration of sodium ion in blood, Cl- represents the concentration of chloride ion in blood, and HCO3- represents the concentration of bicarbonate ion in blood.

3. Under normal circumstances, the unmeasured anion concentration in blood should be very low, and the value of AG should be within the normal range. The range of AG in normal adults is generally between 8-16 mmol/L. If the AG value exceeds the normal range, it may mean that the body has an acid-base imbalance.

Reasons for the increase of AG:

1. Metabolic acidosis: Metabolic acidosis refers to the increase of acidic substances in blood, which leads to the imbalance of blood acid-base balance. Common metabolic acidosis includes diabetic ketoacidosis and lactic acidosis. These diseases will lead to the increase of unmeasured anion concentration in blood, which will lead to the increase of AG.

2. Abnormal renal function: The kidney is an important organ to maintain the acid-base balance of the human body. If the kidney function is abnormal, it will lead to acid-base balance imbalance. Glomerulonephritis, renal tubular acidosis and other diseases will lead to the increase of AG.

3. Poisoning by drugs or poisons: Some drugs or poisons will affect the acid-base balance in the human body, such as methanol poisoning and ethylene glycol poisoning, which will lead to the increase of unmeasured anion concentration in the blood, thus leading to the increase of AG.

4, diarrhea, vomiting, a lot of infusion, etc. These conditions will lead to the imbalance of water and electrolyte in human body, which will lead to the imbalance of acid-base balance and the increase of AG.