An anion gap is calculated by using the results of an electrolyte blood test. This test can help determine what is causing a pH imbalance.

For the body to function normally, it needs to maintain a normal pH balance, or balanced levels of acid and alkali or base in the blood.

When these levels are out of balance, a person may experience symptoms of high acid, otherwise known as acidosis, or high base, known as alkalosis, depending on the underlying cause.

Electrolytes have an electrical charge that helps them maintain the body’s pH level. They are vital for many bodily functions and include substances such as sodium, potassium, chloride, bicarbonate, and other minerals.

Causes of a low anion gap

An electrolyte blood test
An electrolyte blood test is used to calculate an anion gap.

Normally, anion gap results range from 3 to 10 milliequivalents per liter (mEq/L).

Several underlying conditions can result in a pH imbalance and cause an abnormal anion gap.

A low anion gap is very rare. If an electrolyte test shows a low anion gap, a doctor will usually order a second test, as the results may be due to a laboratory error.

Other than a laboratory error, a less common cause of a low anion gap is hypoalbuminemia.

Hypoalbuminemia

Hypoalbuminemia is when a person has too little albumin in their blood. Albumin is an essential protein.

Hypoalbuminemia usually occurs because of inflammation throughout the body.

Causes of hypoalbuminemia include:

Hypoalbuminemia is also considered a contributing factor to having a low anion gap in people with multiple myeloma. It is not known, however, if testing a person’s anion gap is a useful tool for monitoring the progression of the disease.

Causes of a high anion gap

When a person has too much acid or too little base in their blood, the anion gap will be higher than normal. This is called acidosis and can be life-threatening in some situations.

Acidosis can be caused by a variety of conditions, including:

  • some lung disorders, such as severe asthma, sleep apnea, pneumothorax, myasthenia gravis, botulism, amyotrophic lateral sclerosis (ALS), and Guillain-Barre syndrome
  • uncontrolled diabetes or diabetic ketoacidosis
  • kidney damage or failure
  • prolonged diarrhea
  • starvation
  • excessive alcohol use that causes alcoholic ketoacidosis
  • lactic acidosis, which is a buildup of lactic acid
  • exposure to high levels of salicylates (aspirin), methanol, ethylene glycol, or antifreeze
  • drug overdose

Symptoms

young woman yawning while in front of computer
Drowsiness and fatigue can be symptoms of acidosis.

Depending on the cause of the pH imbalance, a person may experience a variety of symptoms.

Conditions associated with a low anion gap are unlikely to cause symptoms. In most cases, the result is from a mistake in the calculation.

Anyone with a low anion gap due to an underlying medical condition will experience the symptoms of that condition.

A person with acidosis may not experience any symptoms or may have nonspecific symptoms related to the underlying medical condition, such as:

When a person has alkalosis or higher levels of base in their blood, they may experience symptoms related to the underlying medical condition, such as:

  • low calcium levels
  • a headache
  • lethargy
  • seizures, muscle spasms, and delirium
  • heart palpitations
  • weakness

Treatment

Treatment for an abnormal anion gap will focus on the underlying cause.

A low or high anion gap alone cannot diagnose a medical condition, so a doctor will perform a variety of other tests before making a treatment plan.

Anyone concerned about a high or low anion gap in their blood test results may find it helpful to speak with a doctor about the potential cause.

Takeaway

A range of underlying medical conditions can affect the body’s pH levels. Calculating the anion gap can help a doctor determine the underlying cause of the abnormality.

A low anion gap is very rare and is often caused by a laboratory error. In this case, a person will require a repeat blood test.

High anion gaps are often associated with serious conditions, such as lung disorders, uncontrolled diabetes, and drug overdose. These conditions need prompt treatment to prevent severe complications, including death.

Anyone who does not understand the underlying cause of a low or high anion gap results should speak to their doctor.