Thick blood - causes, symptoms and treatment

Thick blood - causes, symptoms and treatment

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What is colloquially referred to as “thick blood” is actually medically correct called polyglobulia or erythrocytosis and describes a concentration of red blood cells (erythrocytes) in the blood that is higher than normal. This can pose serious health problems, because the excess of erythrocytes actually causes the blood to become denser, which has a huge impact on its flow properties. Vascular diseases such as thrombosis and bottlenecks in the body's oxygen supply can result. Erythrocytosis also increases the risk of a heart attack or stroke.


Our blood is the main supply fluid for our body and consists of a 90 percent, aqueous solution in which the following substances occur:

  • red blood cells (erythrocytes),
  • white blood cells (leukocytes),
  • Blood plasma,
  • Protein (proteins),
  • Salts.

In addition, there are other substances in the blood, which are only included in molecular size, but reflect the various functions that the blood has in the body. These tasks can be roughly divided as follows:

  • Mass transport: The main task of the blood is to transport important substances to their place of use in the body, including nutrients, oxygen and even hormones. The erythrocytes, which bind the oxygen molecules from the lungs and only release them at their destination in the organism, are responsible for the oxygen transport. At the same time, the blood is also involved in the removal of metabolic breakdown products, including carbon dioxide and urea.
  • Immune defense: The leukocytes in the blood are an essential component of the immune system and are triggered to combat health attacks by foreign bodies (e.g. bacteria or viruses). This happens in several steps, which in addition to the foreign body analysis also includes the production of antibodies. In addition, the blood's coagulation function is an important part of the body's defense against injuries, because blood clotting closes wounds and prevents germs from penetrating the wound opening.
  • Heat regulation: The continuous flow of blood through the body also turns it into a heat conductor. Thanks to the blood circulation, the body temperature can also be regulated. Thereby, both the body's own heat and external heat acting on the organism are regulated.

Erythrocytosis can now have dangerous effects on all functions mentioned. The cause of this is increased blood formation, which significantly increases the number of erythrocytes in the blood. An increased number of erythrocytes becomes clear in the so-called hematocrit value (percentage of blood cells in the blood in percent). This is usually between 37 and 45 percent for women and 42 to 50 percent for men. In the case of erythrocytosis, the value is therefore significantly increased and is visibly more than 50 percent.

Due to the changed consistency of the blood, it actually becomes thicker and can only function to a limited extent or not at all. Circulatory disorders in particular and the associated side effects are typical of blood thickening and can range from visible signs of a lack of oxygen (especially cyanosis) to organ failure due to a lack of oxygen supply. Disorders of the heart and brain function are particularly dangerous in this regard.

Lack of oxygen as the main cause

The causes of erythrocytosis are varied and can be physiological or pathological in nature. Physiologically, the mechanisms of formation of red blood cells play a major role. Their presence in the blood is normally regulated by the hormone erythropoietin (EPO for short), which is formed in the kidney. Since erythrocytes are responsible for the oxygen transport in the blood, the hormone is also controlled via the oxygen content of the blood. If there is insufficient oxygen in the blood over a long period of time, the hormone responds by stimulating the formation of erythrocytes in the bone marrow.

If there is a persistent lack of oxygen in the blood (hypoxemia), the body first tries to compensate for the oxygen level by producing more erythrocytes. Erythropoietin therefore increases, which increases the rate of production of red blood cells, which subsequently leads to physiologically induced erythrocytosis. Various influencing factors can be responsible for such body processes. For example, a longer stay in a low-oxygen environment is conceivable. This is particularly the case for stays at high altitudes of over 4000 meters.

Permanent smoking can also cause erythrocytosis. The reason for this is the fact that the carbon monoxide contained in the cigarette smoke blocks the oxygen binding sites of the erythrocytes and, as a result, they can bind less oxygen. This disturbance lowers the blood oxygen level in the long term. In the area of ​​the causes of the disease, heart diseases such as heart failure or heart valve defects and lung diseases such as bronchial asthma, COPD or pulmonary emphysema are often responsible for hypoxemia.

Speaking of EPO: In Switzerland, researchers recently achieved a breakthrough in the research into the causes of the development of autosomal dominant inherited erythrocytosis. Subjects were members of a family in which about 50 percent of all male and female relatives suffered from thick blood over four generations. A gene defect was identified as the cause, which caused a mutation of the EPO gene.

Tumor diseases and blood oxygen levels

Another factor that can cause erythrocyte production to overshoot is cancer in the blood-forming system. One example is osteomyelofibrosis. Behind this lies a malignant disease of the bone marrow, in which cell degeneration leads to the constant remodeling of bone marrow parts in connective tissue (fibrosis).

Cushing's disease, a tumor of the pituitary gland, cannot be ruled out as the cause of erythrocytosis. The disease results in increased stimulation of the adrenal cortex and thus an increase in cortisone release. Cortisone in turn stimulates the production of red blood cells in the bone marrow. The same applies to various forms of kidney tumors, which trigger similar disorders in the formation of erythrocytes. Last but not least, of course, blood cancer is a disruptive factor that can significantly affect the formation and functionality of red blood cells.

Thromboses promoted by blood thickening also pose a high risk. The latter develop all too readily in the context of erythrocytosis, since blood flow slows down due to the thickened blood and thus causes blood congestion in the veins. Overall, further complications due to illness can be expected.

Other causes

Factors such as massive vomiting and persistent diarrhea are underestimated when it comes to thick blood. Because of the associated loss of fluid in the body, the relative proportions of liquid blood components are greatly reduced in the long term, which can change the material concentration of the blood so that red blood cells take over. Gastrointestinal infections, poisoning and food intolerance are often associated with severe nausea and constant vomiting.

An increased supply of the erythrocyte-forming hormone erythropoietin from the outside cannot be ruled out as the cause of the disease. This occurs primarily through doping with preparations such as EPO or androgens. A relatively rare cause of the disease is also the so-called fetofetal transfusion syndrome - a circulatory and nutritional disorder that only occurs in identical twins in the womb and ensures a mutual blood exchange between the children. A material imbalance in the blood of the affected twins is relatively likely in the context of this syndrome.


The symptoms of erythrocytosis mainly include consequences resulting from insufficient blood oxygen transport. Persistent fatigue and headaches are typical consequences of a lack of oxygen. Cyanosis, a blue coloration of parts of the body due to low-oxygen and therefore darkly discolored blood, is also considered to be typical. Especially the extremities and acra as limbs away from the body are particularly affected by the cyanosis.

Breathing problems and thrombosis caused by blood thickening also pose a high risk. The latter develop all too readily in the context of erythrocytosis, since blood pressure rises rapidly due to the thickened blood and thus causes congestion in the veins. Overall, the following complaints can be expected due to illness:

  • A headache,
  • Dizziness,
  • High blood pressure,
  • increased risk of thrombosis,
  • Cyanosis,
  • Metabolic disorders,
  • Feeling short of breath,
  • Disorders of organ functions.

Warning: If left untreated, erythrocytosis can lead to severe functional disorders of the heart and brain. This increases the risk of stroke and heart attack enormously! Pulmonary embolism can also result from untreated blood thickening.


The diagnosis of thick blood is made in the laboratory by analyzing blood samples. In addition to the hematocrit value, the most important laboratory parameters here are above all the hemoglobin values ​​and the oxygen saturation in the blood vessels. Depending on the focus, further diagnostics are followed by sonographic and cardio-diagnostic procedures (e.g. EKG and cardiac ultrasound). If there is suspicion of a tumor disease, imaging methods such as CT or MRI are also used.


The therapeutic measures against erythrocytosis depend entirely on the underlying cause. If this is due to a genetic defect, there are unfortunately hardly any ways to cure the disease completely. However, there are now very good treatment options for most other influencing factors.

Targeted hydration

If the proportion of erythrocytes is only relatively increased because there are too few liquid components in the blood, the therapy consists of supplying physiological liquid solutions via the vein. Patients should also drink a lot during therapy in order to bring their body's fluid balance back to normal. Such measures are particularly necessary for diarrheal diseases such as gastrointestinal flu.

Oxygen therapy

If the erythrocytosis is based on a hypoxic state, the first measure is usually a supply of high-dose oxygen from the outside. Afterwards, the actual underlying disease has to be treated, which often turns out to be very lengthy in the case of heart and lung diseases, but is not entirely impossible. If smoking was involved in the development of hypoxemia, the therapy measures initiated naturally aim at the permanent abstinence from cigarettes. Support can be provided by appropriate smoking cessation programs as therapy support.

Drug and radiation therapy

Tumor diseases as the cause of the thick blood usually require chemotherapy treatment with medication. Blood cancer in particular cannot be treated surgically, but requires combination therapy of cytostatics and radiation. Promising drugs include drugs such as chlorambuzil, which are often used in conjunction with the antibody obinutuzumab for leukemia. In addition, gene therapies are reporting increasing success in the fight against blood cancer. In addition, blood thinning agents can be administered in erythrocytosis.

Hemodilution therapy

The term hemodilution therapy is the technical term for bloodletting. 300 to 500 ml of blood are taken at regular intervals and replaced with physiological liquid solutions. The goal is to bring the hematocrit back into the normal physiological range through bloodletting. Therapy is usually an emergency solution for illnesses that cannot be treated otherwise. This applies, for example, to genetically caused defects in the EPO gene, but also to untreatable cancers.

Diseases as the cause of thick blood: hypoxemia, blood cancer, Cushing's disease, kidney tumor, osteomyelofibrosis, bronchial asthma, COPD, pulmonary emphysema, fetofetal transfusion syndrome, gastrointestinal infection, poisoning. (Ma)

Author and source information

This text corresponds to the requirements of the medical literature, medical guidelines and current studies and has been checked by medical doctors.

Miriam Adam, Barbara Schindewolf-Lensch


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ICD codes for this disease: D64, D75ICD codes are internationally valid encodings for medical diagnoses. You can find e.g. in doctor's letters or on disability certificates.

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