What Is Thick Blood?

Also Called Hypercoagulability

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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. 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.

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.


Hypercoagulability is the exaggerated tendency of the blood to clot. 

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. Which symptoms are experienced depends on where a clot is forming in the body. These might include:

  • 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

Get emergency medical help right away if you develop any symptoms of a blood clot.


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.


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

  • 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 forming
  • 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 clotting


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

  • Surgery
  • Pregnancy
  • Hormonal contraceptives
  • Hormone replacement therapy
  • Cancer
  • Inflammatory diseases (like lupus)
  • Vascular disease, such as polycythemia (too many red blood cells) 
  • Infection
  • Heparin-induced thrombocytopenia (low platelet count)


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

Since genetics tends to play a strong role in thick blood, your doctor will want to know your family history. Specifically, you will be asked about relatives who have had blood clots or miscarriages.

Blood tests that help your doctor identify hypercoagulation include 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. Further testing may be done to identify suspected underlying conditions. Blood tests may also be used to check for gene mutations.


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

  • 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, doctors often prescribe anticoagulants (blood thinners). 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, doctors may prescribe antithrombin factor to prevent clots in people who have antithrombin III deficiency. Those with protein C deficiency might take protein C.

What Are the Risks?

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

  • 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)


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.

A Word From Verywell

If you have been diagnosed with thick blood, you may be feeling worried. Take heart that many people live with thick blood and can manage it with blood thinners.

Having thick blood puts you at increased risk for blood clots, so managing your condition is important. Remember, thick blood on its own doesn't usually produce symptoms, but blood clots often do.

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.

Frequently Asked Questions

What does thick blood mean?

Thick blood (hypercoagulation) means that a person's body has an exaggerated tendency to clot their blood. In normal circumstances, blood clots when a person is bleeding to prevent too much blood loss. However, with thick blood, clotting occurs even in the absence of bleeding and the clotting is excessive.

Is thick blood bad?

Thick blood is a risk factor for blood clots, so if you have thick blood, you will need to manage it. Unmanaged, thick blood can clot and lead to heart attack, stroke, pulmonary embolism, or deep vein thrombosis.

How do you measure blood thickness?

If your doctor suspects that you have thick blood, you will undergo blood tests to check your red blood cells, white blood cells, platelets, and coagulation times.

6 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Cleveland Clinic. Blood clotting disorders (hypercoagulable states).

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

  3. MedlinePlus. Congenital antithrombin III deficiency.

  4. MedlinePlus. Congenital C or S protein deficiency.

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

  6. Cleveland Clinic. Blood clots.

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.