Also Called Hypercoagulability

By Kathi Valeii 

 Medically reviewed by Richard N. Fogoros, MD

Having thick blood (known as hypercoagulability) means you are at increased risk for developing blood clots. Thick blood isn’t a condition in itself. Rather, it is a result of other vascular conditions.

Thick blood is caused by too many blood cells in circulation or an imbalance in the blood clotting system.1 Thick blood on its own doesn't usually produce symptoms, however, blood clots often do. Learn more about its symptoms, causes, diagnosis, and treatment.

Verywell / Julie Bang

What Is Thick Blood?

Coagulation is the process in which the body forms a clot in response to bleeding. It involves the platelets (specialized cell fragments that circulate in the blood) and various proteins all working together to form a clot and then dissolve it when it is no longer needed.2

When people have thick blood, their blood tends to clot too much or to clot when they are not bleeding. A blood clot (thrombus) that occurs in an artery or vein can be life-threatening. It can block blood flow to essential organs like the brain, heart, and lungs.2

Thick Blood Symptoms

Often, there are no symptoms of thick blood. Most people find out they have thick blood after they have been diagnosed with a blood clot. 

However, sometimes thick blood can produce symptoms that are associated with blood clots. The symptoms experienced depend on where a clot is forming in the body. These might include:3

• Chest pain

• Shortness of breath

• Heart attack symptoms, like arm tingling or pain in the back or jaw

• Headache

• Slurred speech or difficulty speaking

• Dizziness

• Trouble understanding speech

• Pain or redness in the lower leg

Causes of Thick Blood

There are many causes for thick blood. Hypercoagulation can be inherited or a person may develop it due to a health condition. Oftentimes, both genes and the environment are contributing factors.2

Genes

Certain gene mutations that place people at increased risk for developing blood clots include:2

• Gene mutations: Specifically, V Leiden and prothrombin G2021A gene mutations

• Congenital antithrombin III deficiency: A condition in which an abnormal gene results in too little of the protein that prevents abnormal clots from forming4

• Congenital protein C or protein S deficiency: A rare genetic blood-clotting disorder in which the blood lacks sufficient C or S proteins, which help prevent blood clotting5

Acquired 

Exposure to certain hormones, medications, and health conditions can contribute to the development of thick blood. These include:2

• Surgery

• Pregnancy

• Hormonal contraceptives

• Hormone replacement therapy

• Cancer6

• Inflammatory diseases (like lupus)

• Blood disorders, such as polycythemia (too many red blood cells)7

• Infection

• Heparin-induced thrombocytopenia (low platelet count)8

What Are the Risks of Thick Blood?

Thick blood places a person at increased risk for developing blood clots. Blood clots can lead to serious health conditions, including:2

• Heart attack

• Stroke

• Deep vein thrombosis (when a clot develops in one of the body’s larger veins)

• Pulmonary embolism (when a blood clot travels to the lungs)

Diagnosing Thick Blood

If your healthcare provider suspects you have unusual blood-clotting tendencies, they may perform a physical exam, take a detailed medical history, and order some tests. 

Testing may include:

• Genetic tests: Since genetics tends to play a strong role in thick blood, your healthcare provider will want to know your family history. Specifically, you will be asked about relatives who have had blood clots or miscarriages.3

• Blood tests: These are tests that help your healthcare provider identify hypercoagulation including a complete blood count (CBC), coagulation tests that measure your blood's ability to clot and how long that takes, and fibrinogen levels, which are present in blood plasma. Blood tests may also be used to check for gene mutations.3

Further testing may be done to identify suspected underlying conditions.

Treatments for Thick Blood

Treatment for thick blood varies. It depends on whether your healthcare provider is trying to manage an emergency, like an active clot, or working to prevent future clots. Treatment can include:9

• Thrombolytics: Blood clots can lead to emergencies like heart attacks, strokes, pulmonary embolism, and deep vein thrombosis. Emergency care for these situations often includes thrombolytics (medications that break up clots).

• Blood thinners: For management and prevention, healthcare professionals often prescribe anticoagulants (blood thinners). These include medications such as warfarin and heparin. They work by inhibiting blood proteins that are responsible for clotting. These may be taken as a pill, an injection, or intravenously (IV, through a vein).

• Other medications: People with congenital deficiencies may benefit from specific medications to address them. For instance, healthcare professionals may prescribe antithrombin factor to prevent clots in people who have antithrombin III deficiency. Those with protein C deficiency might take protein C.9

You can also take steps to reduce acquired risk factors, such as:9

• Treating medical conditions that can lead to excessive blood clotting

• Quitting smoking

• Losing weight

• Avoiding medications that contain estrogen

• Moving your legs frequently during long trips (to increase blood flow)

Outlook for Thick Blood

For many people with mild forms of thick blood, there are often no complications. For others, treatment can successfully prevent serious conditions like heart attack, stroke, deep vein thrombosis, and pulmonary embolism. However, there may be side effects associated with such medications. For example, those taking blood thinners are at increased risk of bleeding.

That said, it's important to talk with your healthcare provider about your condition and whether or not you should be taking medication to prevent blood clots.2

Summary

Having thick blood (hypercoagulability) means that you are prone to excessive clotting or clotting when you are not bleeding. It can lead to dangerous blood clots that can result in a heart attack, stroke, or other life-threatening problems.

Thick blood can be due to a variety of health conditions, including those you are born with and those you develop after birth. It can be treated with medications. If you notice any dangerous symptoms, such as chest pain, shortness of breath, headache, slurred speech, confusion, or pain in the lower leg, seek medical attention right away.

 Sources

Southeastern Medical Oncology Center. Blood Can Be Too Thin or Too Thick.

Piazza G. Thrombophilia and hypercoagulability. Circulation. 2014;130(2). doi:10.1161/CIRCULATIONAHA.113.007665

American Heart Association. Symptoms and diagnosis of excessive blood clotting (hypercoagulation). 

MedlinePlus. Congenital antithrombin III deficiency.

MedlinePlus. Congenital C or S protein deficiency.

Chiasakul T, Zwicker J. Cancer-associated hypercoagulable state: Causes and mechanisms. UpToDate.

Johns Hopkins Medicine. Polycythemia vera.

Arepally GM, Padmanabhan A. Heparin-induced thrombocytopenia: a focus on thrombosis. ATVB. Published online December 3, 2020. doi:10.1161/ATVBAHA.120.315445

American Heart Association. Prevention and treatment of excessive blood clotting (hypercoagulation). 

By Kathi Valeii
As a freelance writer, Kathi has experience writing both reported features and essays for national publications on the topics of healthcare, advocacy, and education. The bulk of her work centers on parenting, education, health, and social justice.