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How Is Excessive Blood Clotting Diagnosed?

If your doctor thinks that you have excessive blood clotting based on your signs and symptoms, he or she will look for the cause of the condition.

Your doctor will ask about your medical and family histories, do a physical exam, and review the results from tests.

Your primary care doctor may refer you to a hematologist. This is a doctor who specializes in diagnosing and treating blood diseases and disorders.

Medical and Family Histories

Your doctor may ask you detailed questions about your medical history and your family's medical history. He or she may ask whether you or a blood relative:

  • Has a history of repeated blood clots before age 40
  • Has had blood clots during pregnancy or while on birth control pills
  • Has had unexplained miscarriages
  • Has a history of excessive or unusual blood clots (such as clots in the veins in the liver or kidneys)

Physical Exam

Your doctor will do a physical exam to see how severe your blood clotting problem is and to look for a possible cause.

Diagnostic Tests

Your doctor may recommend blood tests to look at your blood cells and the clotting process. If he or she thinks you have a genetic condition, you may need more blood tests.

Tests to find the cause of excessive blood clotting might be delayed for weeks or even months while you receive treatment for a blood clot.

Complete Blood Count and Platelet Count

Initial blood tests will include a complete blood count and a platelet count. These tests measure the number of red blood cells, white blood cells, and platelets in your blood.

In this situation, your doctor will want to know the number of platelets in your blood. Platelets are blood cell fragments that stick together to form clots.

Tests for Clotting Factors and Clotting Time

You also may need blood tests that look at the proteins active in the blood clotting process and how long it takes them to form a blood clot.

Clotting proteins or factors react with each other along two pathways called the intrinsic and extrinsic pathways. (A pathway is a string of chemical reactions that always occur in a certain order.) The two pathways join in a common pathway to make a fibrin network that holds blood clots together.

  • PT test. This test looks at the extrinsic and common pathways to measure how long it takes blood clots to form. People who have excessive blood clotting may take the medicine warfarin to prolong their clotting times.
  • A PTT test. This test looks at the intrinsic and common pathways to measure how long it takes blood clots to form. People also may take blood thinners, like heparin, to slow their clotting times.

Followup Tests

If your doctor thinks your blood clotting condition is genetic, you may need other blood tests. For example, you might need tests to check:

  • For gene mutations that can cause excessive blood clotting
  • For antibodies related to antiphospholipid antibody syndrome—a cause of excessive blood clotting
  • Your homocysteine levels (if you're at risk for vascular disease)
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Clinical trials are research studies that explore whether a medical strategy, treatment, or device is safe and effective for humans. To find clinical trials that are currently underway for Excessive Blood Clotting, visit www.clinicaltrials.gov.


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May 30, 2012 Last Updated Icon

The NHLBI updates Health Topics articles on a biennial cycle based on a thorough review of research findings and new literature. The articles also are updated as needed if important new research is published. The date on each Health Topics article reflects when the content was originally posted or last revised.