Blood relies on a balance to maintain a normal consistency. If an imbalance in the proteins and cells develops, your blood can become too thick. This is known as hypercoagulability.

While a person’s blood may look uniform, it’s made of a combination of different cells, proteins, and clotting factors, or substances that aid clotting.

A number of factors can cause thick blood, such as:

  • excess blood cells in circulation
  • diseases that affect blood clotting
  • excess clotting proteins in the blood

Because there are so many potential causes of thick blood, doctors don’t have a standard definition of thick blood. They instead define it through each condition that results in thick blood.

Blood clotting disorders that cause thick blood tend to be rare. Some of the more common include factor V Leiden, which an estimated 3 to 7 percent of the general population has. This condition doesn’t mean a person’s blood will be too thick, but that they are predisposed to having thick blood.

Of all the people who’ve had a blood clot in their veins, less than 15 percent are due to a condition that causes thick blood.

Many don’t have any symptoms of thick blood until they experience a blood clot. The blood clot usually occurs in a person’s vein, which can cause pain and affect circulation in and around the area where the clot occurs.

Some are aware they have a family history of a blood clotting disorder. This may motivate them to be tested for blood clotting issues before any arise.

Having too many blood cells can lead to a variety of symptoms. Examples of these include:

If you experience any of these symptoms, you should see your doctor to test for thick blood:

  • having a blood clot of unknown origin
  • having repeated blood clots for no known reason
  • experiencing recurrent pregnancy loss (loss of more than three first-trimester pregnancies)

Your doctor may order a variety of blood screening tests if you have these symptoms in addition to a family history of thick blood.

The conditions that result in thick blood can be inherited or acquired at a later time, as is usually the case with cancers. Following is small sample of the many conditions that can cause thick blood:

It’s important to understand that conditions that cause thick blood, and sometimes blood clotting, aren’t the only causes of blood clots.

For example, a person may experience a heart attack because their blood came in contact with plaque in their arteries, which causes a clot to form. Those with poor circulation also are more prone to blood clots because their blood doesn’t move through their bodies as well. This isn’t due to the blood’s thickness. Instead, the arteries and veins of these people are damaged, so blood can’t move as fast as normal.

Your doctor will start the diagnostic process by taking your medical history. They will ask questions about any symptoms you may be experiencing as well as a health history.

Your doctor will likely order blood testing, but usually in stages. The reason for this is that many of the tests for thick blood are costly and very specific. So they will start with more common tests, and then order more specific ones if necessary.

An example of some of the blood tests used if your doctor thinks you may have thick blood include:

  • Complete blood count: This test screens for the presence of red blood cells and platelets in the blood. High hemoglobin and hematocrit levels could indicate the presence of a condition like polycythemia vera.
  • Activated protein C resistance: This tests for the presence of factor V Leiden.
  • Prothrombin G20210A mutation testing: This determines the presence of antithrombin, protein C, or protein S abnormalities.
  • Antithrombin, protein C, or protein S functional levels: This can confirm the presence of lupus anticoagulants.

The Cleveland Clinic recommends that testing for thick blood occur at least four to six weeks after you have a blood clot. Testing sooner could lead to a false-positive result due to the presence of inflammatory components in the blood from the clot.

The treatments for thick blood depend upon the underlying cause.

Polycythemia vera

While doctors can’t cure polycythemia vera, they can recommend treatments to improve blood flow. Physical activity can help promote proper blood flow through your body. Other steps to take include:

  • frequently stretching, especially of your legs and feet to promote blood flow
  • wearing protective clothing, especially for your hands and feet, during winter
  • avoiding extremes of temperature
  • staying hydrated and drinking plenty of fluids
  • taking starch baths by adding a half-box of starch to lukewarm bathwater, which can soothe the often-itchy skin associated with polycythemia vera

Your doctor may recommend a treatment approach called phlebotomy, where they insert an intravenous (IV) line into a vein to remove a certain amount of blood.

Several treatments help to remove some of your body’s iron, which can reduce blood production.

In rare instances, when the condition causes severe complications, such as organ damage, your doctor may recommend chemotherapy medications. Examples of these include hydroxyurea (Droxia) and interferon-alpha. These help to stop your bone marrow from producing excess blood cells. As a result, your blood becomes less thick.

Treatment for conditions that affect blood clotting

If you have a disease that causes blood to clot too easily (like factor V mutations), your doctor may recommend some of the following treatments:

  • Antiplatelet therapy: This includes taking medications that prevent blood cells responsible for clotting, called platelets, from sticking together to become a clot. Examples of these could include aspirin (Bufferin).
  • Anticoagulation therapy: This involves taking medications used to prevent blood clots, such as warfarin (Coumadin).

However, many people who have conditions that could make their blood thick never experience a blood clot. For this reason, your doctor may diagnose thick blood, yet not prescribe a medication for you to take regularly unless they believe you’re truly at risk for a clot.

If you’re prone to blood clots, you should engage in lifestyle measures known to reduce their likelihood. These include:

  • refraining from smoking
  • engaging in regular physical activity
  • taking frequent opportunities to stretch and walk when traveling long distances on a plane or by car
  • staying hydrated

If you have thick blood, you’re at greater risks for blood clots, both in your veins and arteries. Blood clots in your veins will impact blood flow to key areas of your body. Without enough blood flow, tissues can’t survive. If you think you may have a blood clot, seek immediate medical treatment.

One of the most potentially deadly effects of thick blood is pulmonary emboli, which are blood clots that block one or more of the pulmonary arteries in the lungs. As a result, the lung can’t get oxygenated blood. The symptoms of this condition include shortness of breath, chest pain, and a cough that may have blood present. You should seek emergency medical treatment if you think you could have pulmonary emboli.

According to the Cleveland Clinic, there is currently no data to suggest that thick blood affects life expectancy. However, if your family has a history of the condition, you may want to consult your doctor about possible risks.