Methaemoglobinemia is when there is an increased level of methemoglobin in the blood. Methemoglobin is a derivative of hemoglobin, which gives red blood cells their color and binds oxygen for transport around the body. Since methemoglobin cannot bind oxygen, there is a systemic undersupply of oxygen in methemoglobinemia, which becomes noticeable, among other things, through bluish discoloration of the skin, tiredness and dizziness.
What is methemoglobinemia?
Methaemoglobinemia occurs when the proportion of methemoglobin in the total hemoglobin content of the blood exceeds its physiological value. A precise threshold value is not defined. In a healthy person, the proportion of methemoglobin is around 3%. The first clinical symptoms appear from about 10%, serious tissue hypoxia from 30% (especially in the brain). See AbbreviationFinder for abbreviations related to Methemoglobinemia.
From 40% methemoglobin content there is danger to life. Hemoglobin (Hb) is a protein made up of 4 subunits. Embedded in each subunit is an iron atom in oxidation state II, which can bind and donate oxygen molecules. When the divalent iron atom is oxidized to a trivalent iron atom, methemoglobin (MetHb) is formed.
Methaemoglobin is not only unable to bind oxygen itself, but also influences the hemoglobin in its environment in such a way that it only binds oxygen but no longer releases it. Methaemoglobinemia therefore endangers the oxygen supply of the entire organism.
A basic distinction is made between congenital methemoglobinemia and acquired methemoglobinemia. The congenital variant is due to genetic defects in hemoglobin or in enzymes that prevent oxidation of hemoglobin, but is very rare.
Much more frequently, methemoglobinemia is caused by intoxication. Many different substances can be considered as triggers: In everyday clinical practice, methaemoglobinaemia occurs most frequently after the administration of certain medications, including dapsone and local anesthetics of the amide type. Aromatic compounds in dyes (e.g. aniline) and nitrite compounds are also known triggers.
Nitrite poisoning is caused, for example, by pickling salt, spinach dishes that are not refrigerated or when preparing baby food with water containing nitrate. Accumulated cases of methaemoglobinaemia in infants (so-called infant blue fever) in the 1950s and 1960s led to the introduction of nitrate limits in drinking water in Germany.
Symptoms, Ailments & Signs
Which symptoms occur with this disease and how they develop depends on the one hand on the age of the patient. On the other hand, underlying heart or vascular diseases also influence the severity of the symptoms. If the methemoglobin level in the blood remains below three percent, those affected usually have no symptoms at all.
When the three percent is exceeded, the first signs of oxygen deficiency appear. This can be a headache, lightheadedness or shortness of breath. In addition, the skin becomes paler and takes on a greyish color. If the MetHB concentration rises above ten percent, the skin and mucous membranes become bluish ( cyanosis ) and the arterial blood is clearly undersupplied with oxygen (hypoxemia).
From a proportion of about 30-50 percent MetHB in the blood, severe breathing disorders must be expected, and the vascular functions are also restricted. The blood turns dark and takes on a chocolate-like color. The dizziness increases, there may be a brief loss of consciousness and a pronounced feeling of weakness.
If the concentration increases to over 50 percent, the brain can no longer be supplied with sufficient oxygen and neurological disorders appear. The patient falls into deep unconsciousness, the heart reacts with arrhythmias. Above 70 percent MetHB in the blood, there is a high probability of death.
Diagnosis & History
The first sign of methemoglobinemia is cyanosis, ie a bluish to greyish discoloration of the skin. This is particularly noticeable on the lips and mucous membranes.
The methemoglobin itself is brown in color; therefore, blood freshly drawn during methemoglobinemia appears chocolate brown. Other symptoms are dizziness, tiredness, impaired consciousness, shortness of breath and an accelerated heartbeat ( tachycardia ). The diagnosis of methemoglobinemia is confirmed by a spectroscopic blood test.
There is also a simple bedside test in which a drop of normal blood and a drop of patient blood are placed side by side on filter paper and compared one minute later. With methemoglobinemia, the patient’s blood retains its characteristic brown color. A pulse oximetry measurement of oxygen saturation can be misleading:
This shows a high oxygen saturation even in severe methaemoglobinemia. Untreated methemoglobinemia can be fatal if the lack of oxygen is so severe and prolonged that tissue dies. The brain and kidneys are particularly sensitive.
Methaemoglobinemia primarily leads to a severely reduced supply of oxygen in the patient. This undersupply has a very negative effect on the overall health of the patient and can significantly reduce the quality of life. In most cases, the internal organs are also damaged by this undersupply.
Those affected also suffer from headaches and fatigue, although in severe cases the methaemoglobinemia can also lead to shortness of breath. Furthermore, the brain is also damaged by the lack of supply. As the disease progresses, there is a loss of consciousness and possible injury if a fall occurs.
Those affected suffer from a disturbance of consciousness and a blue discoloration of the skin. The resilience of those affected is significantly reduced by the methaemoglobinemia, so that the execution of usual activities or professions can also be restricted. As a rule, methemoglobinemia can be treated relatively easily and quickly, so that in most cases there are no complications or consequential damage.
Complications usually occur when treatment is not provided and the undersupply lasts for a long period of time. Therefore, life expectancy is usually not reduced by methaemoglobinemia.
When should you go to the doctor?
If the person concerned suffers from diffuse symptoms that cause a general feeling of discomfort or illness, a doctor should be consulted. If there is a gradual increase in symptoms over several months, medical clarification of the cause is required. Discoloration of the skin, blue lips or shortness of breath are signs of an existing condition that needs to be investigated and treated. If headaches, dizziness or tiredness occur repeatedly, it is advisable to consult a doctor. A decrease in performance, exhaustion or rapid fatigue when performing everyday tasks indicate a health impairment.
A doctor must be consulted so that a comprehensive examination can take place. If there is a disturbance of consciousness, there is cause for concern. In the event of a loss of consciousness, an emergency doctor must be alerted. If left untreated, methaemoglobinemia can lead to premature death.
Therefore, in the event of cardiac arrhythmias, an increased heart rate and a feeling of oxygen deficiency in the body, medical checks should be carried out in good time. A doctor is needed for sleep disorders, general dysfunction or a loss of well-being.
Treatment & Therapy
The prognosis of methemoglobinemia is usually good. Slight intoxications resolve on their own provided the toxic substance is no longer administered.
The basis of this regression is the fact that in the human body erythrocytes are constantly broken down and newly formed (about two million per second) and the poisoned erythrocytes are exchanged in this way. For severe poisoning, therapy consists of oxygen and intravenous solutions containing redox dyes such as methylene blue or toluidine blue.
In very severe cases, a blood transfusion may also be necessary. Another antidote is ascorbic acid ( vitamin C ). Daily doses of vitamin C are the drug of choice for hereditary methaemoglobinemia; these are not curable, but can only be alleviated.
Outlook & Forecast
The prognosis of methemoglobinemia is usually favorable. Medical care is not necessary for all patients. In some cases, spontaneous healing occurs, so that no further action is required. If the disease is due to the administration of medication, changing the preparations prescribed can already contribute to recovery from the methemoglobinemia.
However, if there is a genetic disease, the person affected will need drug treatment over the course of their life so that their situation can be improved. The therapy helps to optimize the proportion of methemoglobin in the blood and to meet the needs of the organism. The patient must expect to participate in long-term therapy, otherwise the symptoms will return within a few weeks or months.
Without seeking medical care, the quality of life of those affected by a genetic disease is limited over their entire lifespan. In these cases, the prognosis is worse because of the symptoms. In acute phases or in the case of severe disease progression, only a blood transfusion can ultimately alleviate the symptoms. Here, too, it is possible that this measure will have to be resorted to several times in the course of life, since it is only a question of a temporary improvement in health.
The main way to prevent methemoglobinemia is to avoid exposure to toxic triggers. Infants, who are particularly susceptible to methemoglobinemia, must avoid consuming foods high in nitrites.
Follow-up care for methemoglobinemia is similar to preventive care. It is therefore primarily about treating the causative disease. In order to minimize the risk in children, parents should ensure that breathing is not restricted by mechanical influences.
In general, follow-up care is based on whether the disease is congenital and whether it was caused by poisoning. Adults over the age of 35 are advised to have regular check-ups. These tests can be used to detect changes and abnormalities at an early stage so that rapid therapy can be initiated.
You can do that yourself
In the case of methemoglobinemia, it is usually sufficient to avoid the triggering substance. Patients who regularly take medication should switch to another drug or reduce the dose in consultation with their doctor. If the typical symptoms occur as a result of excessive intake of curing salt or spinach dishes, a doctor’s visit is also indicated.
Those affected should also change their diet and speak to a nutritionist if symptoms persist. Each symptom must be treated individually. Sleep and gentle sedatives and painkillers from naturopathy help with headaches and tiredness. Dizziness and confusion can usually be relieved by exercising in the fresh air. Depending on the intensity of the symptoms, bed rest and rest are also indicated.
If complications occur, you must definitely go to a hospital with methemoglobinemia. Eating an adequate diet and drinking plenty of fluids is important before treating methemoglobinemia. Otherwise, circulatory shock and symptoms such as fever can occur. After the therapy, the affected person is initially given bed rest and rest. The doctor in charge can give further tips on how the symptoms can best be overcome.