The health issue that causes thick blood may be inherited or genetic, or it may be acquired, developing over time. Some medical conditions that cause the blood to thicken include:
Polycythemia vera (PV) is a blood disorder that originates in bone marrow, the soft center of the bone where new blood cells develop. PV involves the bone marrow making too many red or white blood cells and platelets, causing the blood to thicken.
Experts believe that PV results from genetic changes that occur after conception. It is not generally inherited, in other words, the changes tend to occur slowly over many years.
Various symptoms may appear over time, including:
- sweating, especially at night
- itchy skin
- blurred vision and ringing in the ears
- abdominal fullness or bloating, due to an enlarged spleen
PV affects 44-57 people in every 100,000, and it usually appears after the age of 60 years, according to the National Organization for Rare Disorders.
Find out more about polycythemia vera — and secondary polycythemia.
Waldenström macroglobulinemia is a rare type of non-Hodgkin lymphoma. The body produces large amounts of the antibody protein called immunoglobulin M. This can cause the blood to become thick, resulting in a range of symptoms.
The symptoms vary, but they may include:
- bleeding in the gums and the retinas of the eyes as small blood vessels become damaged
- tingling and numbness in the fingers and toes
There are about 1,000 to 1,500 new diagnoses of Waldenström macroglobulinemia in the United States each year, according to the American Cancer Society.
Lupus, including systemic lupus erythematosus
According to the Lupus Foundation of America, 1.5 million people in the U.S. live with some form of lupus.
Common symptoms include:
- joint pain and swelling
Systemic lupus erythematosus (SLE) is an inflammatory disease that happens when the immune system attacks healthy tissues as if they were diseased. It can affect the blood in many ways, including increasing the risk of clotting.
Thrombosis — a blood clot blocking a blood vessel — is relatively common in the first year of living with SLE. This may result from increased disease activity, including high levels of inflammation and other factors.
Find out more about SLE.
Factor V Leiden
This results from a genetic change that increases the risk of blood clots, especially in deep veins.
In most people, a protein called activated protein C regulates the activity of the clotting factor called factor V. In people with this condition, protein C cannot regulate factor V’s activity, resulting in thick blood and a risk of clotting.
Unregulated factor V activity leads to excessive clotting and thickened blood.
Deficiencies in proteins C and S and antithrombin
The body produces natural anticoagulants, such as proteins C and S and antithrombin. Some people have low levels of these substances, leading to a higher risk of blood clots. This may result from an inherited health issue or develop over time.
The first sign of this issue is often a blood clot. The doctor may find this during a test. If a clot forms in a deep vein, the doctor may diagnose deep vein thrombosis (DVT). If a clot breaks off and travels to block a blood vessel that supplies blood to the lungs, this is called a pulmonary embolism (PE), and it is life threatening.Protein C deficiency affects around 1 in 200-500 people, protein S deficiency 1 in 500 people, and antithrombin deficiency 1 in 2,000-5,000 people.
Learn more about protein C deficiency.
Prothrombin gene 20210A mutation
People with this genetic feature have too much of the blood-clotting protein factor II, also called prothrombin. Prothrombin is one factor that enables blood to clot correctly, but too much prothrombin can increase the risk of clots forming, including those responsible for DVT and PEs.
The mutation affects 2-4% of Americans of European ancestry and around 0.4% of African Americans, according to the National Blood Clot Alliance.
Thick blood can develop over a lifetime due to environmental factors or health conditions.
Risk factors include:
- exercise, in people with certain blood and cardiovascular conditions
- hormonal changes, for example, during pregnancy
- hormonal medications, such as some forms of birth control, hormone replacement therapy, and testosterone therapy
- inflammation, possibly caused by SLE or inflammatory bowel disease
- trauma and injury
- some diseases, such as cancer, particularly multiple myeloma