Medical News Today: What is methemoglobinemia?

Methemoglobinemia is a blood disorder that occurs when too little oxygen is delivered to the cells of the body. There are two kinds of methemoglobinemia — congenital and acquired.

Methemoglobinemia (MetHb) is pronounced met-he-mo-glo-bi-ne-mia.

Babies can inherit it from their parents; this is called congenital MetHb. Sometimes it is called blue baby syndrome, as one of the symptoms can be a blue tinge to the skin.

People can develop acquired MetHb after exposure to certain drugs or chemicals. Acquired MetHb is also rare, but it is usually mild and resolves after the person has identified and removed the cause.

How is it treated?

Methylene blue in centrifuge.
Methylene blue is sometimes used to treat serious cases of MetHb.

Some people with congenital MetHb do not have any symptoms, meaning they may not need treatment.

Mild cases of acquired MetHb do not usually require treatment either. A doctor will advise the person to avoid the substance that caused the problem.

Methylene blue is used to treat severe cases of MetHb, and doctors may prescribe ascorbic acid to reduce the level of methemoglobin in the blood.

In severe cases, a person may require a blood transfusion or exchange transfusion. Oxygen therapy will also be provided, if required.

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How is it diagnosed?

A doctor will diagnose the condition using a blood test that checks the level of functional hemoglobin in the blood.

A doctor may carry out pulse oximetry, which checks the oxygen level of the blood, and a blood test that checks the concentration of gases in the blood.

Types of methemoglobinemia

The condition occurs when the blood protein hemoglobin in a person’s body converts into methemoglobin.

Hemoglobin is present in red blood cells to carry oxygen around the body, distributing it to all the tissues and organs that need it to survive.

When a person has MetHb, the oxygen is still carried around the body but is not released effectively.

Inherited MetHb

MetHb can be passed down if one or both parents carry a faulty gene that causes problems with the enzyme cytochrome b5 reductase.

  • Type 1 inherited MetHB: This is also called erythrocyte reductase deficiency and occurs when the red blood cells do not have cytochrome b5 reductase.
  • Type 2 inherited MetHB: is also called generalized reductase deficiency, and this occurs when many cells in the body do not have the enzyme.
  • Hemoglobin M disease: This occurs when the hemoglobin protein itself is defective.

Acquired MetHB:

Acquired MetHb is more common than the inherited forms and is caused by exposure to:

  • anesthetics, such as benzocaine
  • nitrobenzene
  • some antibiotics, including dapsone and chloroquine
  • nitrites, which are used as additives to prevent meat from spoiling
  • some foods, such as spinach, beets, or carrots, contain natural nitrates which can cause MetHb if consumed in large amounts

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What are the symptoms?

Cyanosis, or blue skin, on person's foot. Symptom of methemoglobinemia and argyria.
Cyanosis, or blue skin, is a potential symptom of methemoglobinemia.

A baby born with the condition may have a bluish tinge to their skin, which is called cyanosis. This color might be apparent at birth or shortly afterward.

They may show signs of:

  • blueness around the mouth
  • blueness around the hands
  • blueness around the and feet
  • have difficulties breathing
  • vomiting
  • diarrhea

In severe cases, they may be:

  • extremely lethargic
  • salivate excessively
  • lose consciousness.

Symptoms vary according to the amount of methemoglobin in the blood, which is measured on a scale called the MetHb concentration.

The normal level of MetHb concentration in a person’s blood is between 0 and 3 percent. If MetHb reaches a concentration of 3 to 10 percent, a person’s skin may take on a blue-grey appearance of cyanosis.

MetHb levels of 15 to 30 percent lead to cyanosis, where blood starts to look chocolate brown.

Concentrations of 30 to 50 percent start to cause more severe symptoms. These symptoms may include a headache, fatigue dizziness, anxiety, and confusion, as well as temporary loss of consciousness, rapid heartbeat, and weakness.

When levels reach 50 to 70 percent, the person may experience seizures, kidney problems, or an abnormal heartbeat.

MetHb concentrations of 70 percent and over can be fatal.

Typical symptoms of the different types of MetHb are:

Type 1 MetHb:

  • bluish coloring of the skin

Type 2 MetHb:

  • developmental delay
  • learning difficulties
  • seizures

Hemoglobin M disease

  • bluish coloring of the skin

Acquired MetHB:

  • bluish coloring of the skin
  • headache
  • fatigue
  • shortness of breath
  • lack of energy

What causes MetHb?

Doctor speaking to couple to help with family planning.
MetHb can be inherited, so people with a family history of the condition should seek professional medical advice when planning a family.

The cause of MetHb is dependent on what type it is. MetHb can be congenital, meaning it is inherited or acquired, which means it is caused by exposure to certain drugs, chemicals or foods.

What are the possible complications?

Methylene blue, which is used to treat severe forms of MetHb, can be unsafe for people who have or are at risk of developing a disease called G6PD deficiency.

Cases of severe MetHb can lead to shock, seizures, and even death.

Can it be prevented?

Congenital MetHb cannot be prevented. People with a family history of the blood disorder are advised to request genetic counseling from a healthcare professional before starting a family.

To prevent acquired MethHb, people should avoid known causes, such as benzocaine, which is one of the most common initiators. Benzocaine is present in many over-the-counter medications, but the topical sprays containing the anesthetic benzocaine cause most of the severe cases.

Children under 6 months should not eat foods containing nitrates, such as spinach, beets or carrots.

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Congenital type 2 MetHb can be serious and often leads to death in the first few years of life. As such, people with a family history of the condition are advised to speak to a healthcare professional before having children.

People with type 1 MetHb and hemoglobin disease tend to do well. Acquired MetHb can be fatal, but once the cause of the problem has been identified and removed, outcomes are good. Most cases will not even require treatment.

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