There's a saying that "blood is thicker than water," but blood that is too thick can be a serious medical issue. Although uncommon, there are some disorders that cause thick blood -- including those that lead to an abnormally high number of blood cells and conditions that cause hypercoagulation, or excessive blood clotting. These disorders can lead to serious, life-threatening consequences, so early detection and treatment are important.
Excess Blood Cells
Certain diseases, namely blood cancers, thicken the blood because they lead to abnormally high levels of blood cells. While rare, one of the more common reasons for thick blood is called polycythemia vera (PV), in which the body produces excessive blood cells -- mostly too many red blood cells. PV is caused by a genetic mutation and typically develops slowly, over several years.
Waldenstrom macroglobulinemia is a type of non-Hodgkin lymphoma, or blood cancer, that causes overproduction of an antibody -- a type of blood protein -- called immunoglobulin M. Myeloma is a blood cancer caused by abnormal and uncontrolled growth of plasma cells -- a type of white blood cell that produces antibodies. These conditions can also cause thick blood, crowding the blood with abnormal antibodies, leaving too few of the infection-fighting antibodies.
When you suffer a wound or cut, your body forms a blood clot to stop the bleeding -- a process called coagulation. The clot is formed from blood proteins called fibrins and platelets, or cell fragments. Typically, your body breaks down the clot. However, sometimes blood clots form too easily or do not dissolve properly. This excessive clotting -- hypercoagulation -- also causes thick blood. This can be dangerous since clots can form inside your blood vessels and block blood flow to tissues or organs. Hypercoagulation may be caused by genetic disorders or it may be associated with acquired conditions such as certain autoimmune diseases and cancers, pregnancy or certain medications.
Thick blood flows more slowly than normal blood, which deprives body organs and tissues of the amount of oxygen required for necessary function. Side effects include headaches, dizziness, fatigue, itchiness and vision problems. High levels of abnormal white blood cells can cause anemia, tiredness, weight loss, bone pain and frequent infections. Most seriously, people with thick blood -- whether from excessive blood cells or hypercoagulation -- are at high risk for clots that block or limit blood flow to vital organs. The possible consequences include a stroke, heart attack or serious damage to other organs such as the kidneys or lungs.
Many people are not diagnosed with these conditions until later in life. However, sometimes these disorders are uncovered by routine blood tests, through personal or family medical histories or when a doctor is investigating the cause of early symptoms such as tiredness or anemia. Depending on the severity and underlying cause of thick blood, there may be ways to correct the disorder or reduce the risk of related complications. Phlebotomy -- the removal of some blood -- or medications are treatments aimed at reducing blood cell numbers. Blood thinning medications such as warfarin (Coumadin) can reduce clotting. Consultation with a physician specializing in blood disorders will determine the best course of action for your specific condition.
Most importantly, immediate medical care is needed if a blood clot, stroke or heart attack is suspected. A blood clot in the leg can cause redness, pain, warmth and swelling in the lower leg. A heart attack or a blood clot in the lungs or heart can cause shortness of breath, chest pain, chest heaviness or pressure and discomfort in the neck, jaw, upper back or arms. Symptoms of a stroke include difficulty speaking or understanding speech, headaches or paralysis that is typically on one side of the body. These symptoms require emergency medical care to determine the cause and receive live-saving treatment as soon as possible.
- National Heart, Lung, and Blood Institute: What Is Polycythemia Vera?
- National Heart, Lung, and Blood Institute: What Are the Signs and Symptoms of Polycythemia Vera?
- American Heart Association: What Is Excessive Blood Clotting (Hypercoagulation)?
- Annals of Hematology: Current and Future Treatment Options for Polycythemia Vera
- Leukemia and Lymphoma Society: Waldenström Macroglobulinemia Facts