Methemoglobinemia - Causes, Symptoms, Diagnosis, and Treatment

What Is Methemoglobin?

Methemoglobin is a metalloprotein form of hemoglobin. It is not able to bind to the oxygen. It does not have enough capacity to carry oxygen. The normal range of methemoglobin is 0-3%. Higher levels of methemoglobin can reach up to 15%. When your body is producing too much of methemoglobin, it will start replacing the normally present hemoglobin. This can cause oxygen to be removed from the cells. The level of methemoglobin can be determined by blood cell count and examination of the color.

What Is Methemoglobinemia?

Methemoglobinemia is a blood disorder. An abnormal amount of methemoglobin is produced in this condition. Hemoglobin is the protein in red blood cells (RBCs) that carries and distributes oxygen to the body. In methemoglobinemia, the hemoglobin is still able to carry the oxygen but cannot release it efficiently to the tissues of the body.

What Are the Symptoms of Methemoglobinemia?

The symptoms might change based on the variant of methemoglobinemia. When the level of methemoglobin rises, symptoms begin to get worse. The common symptoms are:

• Cyanosis. It involves the bluish discoloration of the skin and mucous membrane. This occurs due to the deoxygenation of the blood. There will be an elevation in deoxyhemoglobin levels. This will be most prominently evident in lips and fingers. Because of the cyanosis in methemoglobinemia, this condition is referred to as “Blue baby syndrome.” The connection between high nitrate levels and the blue baby syndrome is the water level crossing the standard limit of 10 mg/L

• Blood becomes chocolate brown in color.

• Rapid heart rate.

• Dyspnea (Shortness of breath).

• Nausea.

• Headache.

• Lethargy.

• Fatigue.

• Confusion.

• Loss of consciousness.

Based on the concentration, the signs and symptoms shown may vary.

0-3 % - No symptoms will be shown.

10-20 % - Mild symptoms.

20-50 % - Decreased exercise tolerance, tachycardia, fatigue, and dyspnea.

Higher than 50 % - Seizure, hypoxia, coma, and metabolic acidosis.

Higher than 70 % - Severe hypoxia and death.

What Are the Types of Methemoglobinemia?

• Depending on the duration of the condition, it may be classified as acute or chronic.

• Depending on the cause of the condition, methemoglobinemia is of different types. The congenital methemoglobinemia is divided into two types. It is hereditary or acquired. This genetic defect is accompanied by a deficiency of either an enzyme or a protein responsible for converting methemoglobin to hemoglobin.

• Type 1: It occurs when there is a lack of enzymes in the red blood cells. It is also called erythrocyte reductase deficiency. In type 1, both the parents are just the carriers of the gene involved.

• Type 2: It occurs when the enzymes do not work so well in your body. It is also called generalized reductase deficiency. A poor activity of the reductase enzyme is noted. The abnormal gene is inherited from one parent only.

The acquired type is due to the problem in hemoglobin itself. The acquired type is more common than the inherited type. It is an acute condition.

What Are the Causes?

The acquired type occurs in some people due to the exposure of harmful chemicals and medicines. The commonly involved chemicals, food, and medications are:

• Nitrates: Babies who are younger than six months may develop acquired methemoglobinemia from the excess of nitrites present in the contaminated water. The bacterial flora present in the baby’s digestive system adversely reacts with the nitrates and causes methemoglobinemia. Completely developed digestive systems can avoid this kind of nitrate poisoning.

• Nitrobenzene.

• Benzocaine: Benzocaine over-the-counter product. It is used to soothe sore gums of the baby. The U.S.Food and Drug Administration organization has advised the baby-sitters, parents, and caregivers not to use them.

• Medications like Dapsone. This medication is used to treat dermatitis, acne, and blisters in the arms and buttock region. It is also known to be useful for fungal infections in the lungs of HIV patients.

• Antimalarial drugs like Chloroquine.

• Solid foods: Certain home foods, including fruits and vegetables like beetroot, carrots, spinach, and beans, are known to have high nitrates. So, these kinds of solid foods are not advised for children. Parental counseling therapy includes food that can be fed to babies. In this therapy, parents are advised not to give babies solid foods before they are four months old.

What Are the Risk Factors?

The risk increases when the patient is suffering from comorbid conditions such as anemia, lung disease, sepsis, and cardiovascular disease. It is also associated with the presence of abnormal hemoglobin, such as sulfhemoglobin and sickle hemoglobin.

What Are the Complications?

• Seizures.

• Bronchitis.

• Asthma.

• Emphysema.

• Heart arrhythmias.

• Death. (This can occur in patients having methemoglobin level more than 70%).

How Is It Diagnosed?

1. The Potassium Cyanide Test: This test is used for differentiating methemoglobin and sulfhemoglobin. When a few drops of potassium cyanide is added, methemoglobin turns to bright red, but sulfhemoglobin does not change color and remains dark brown.

2. Clinical Examination: The characteristic chocolate brown color blood is noted.

3. Blood Examination: Complete blood count is done to note the nitrates level in the blood and other drugs.

4. Arterial Blood Gas Analysis: This is a method used to periodically check the saturation levels of oxygen, carbon-dioxide, and bicarbonate.

5. Pulse Oximetry: This is used to identify the level of oxygen saturation in the blood. It is a non-invasive diagnostic method.

6. DNA Sequencing: It is the process in which determining the nucleic acid sequence is done. It identifies the order of nucleotides in DNA molecules. It includes various technological methods to find the order of the four bases, such as adenine, guanine, cytosine, and thymine.

What Is the Treatment?

• Chronic methemoglobinemia requires medications to reduce cyanosis. Methylene blue and Citric acid are known to be helpful. Treatment involves infusion with the drug Methylene blue. In congenital conditions, Methylene blue cannot be used. Such patients might require Aspirin therapy.

• Severe and acute conditions are life-threatening and require additional therapeutic methods. It is a medical emergency.

How Is the Prognosis?

The prognosis level decides the prediction level to show whether the condition will improve or not. The prognosis for methemoglobinemia is relatively very poor.

What Is the Differential Diagnosis?

• Heart failure.

• Sulfhemoglobinemia.

• Argyria.

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