Symptoms and Diagnosis of Excessive Blood Clotting (Hypercoagulation)

Many factors can lead to excessive blood clotting, causing limited or blocked blood flow and can be life-threatening. Signs and symptoms of excessive blood clotting depend on where the clots form.

  • A blood clot in the heart or lungs could include symptoms such as chest pain, shortness of breath, and upper body discomfort in the arms, back, neck, or jaw, suggesting a heart attack or pulmonary embolism (PE).
  • A blood clot in the brain could cause headaches, speech changes, paralysis (an inability to move), dizziness, and trouble speaking or understanding speech, suggesting a possible stroke.
  • A blood clot in the deep veins of the leg may create symptoms such as pain, redness, warmth, and swelling in the lower leg, and could suggest deep vein thrombosis (DVT) or peripheral artery disease (PAD).  If you have signs or symptoms of a heart attack, PE or stroke, call 911 right away. If you have signs or symptoms of DVT, call your doctor right away. The cause of the blood clot needs to be found and treated as soon as possible.

Diagnosis

If your healthcare provider thinks that you have excessive blood clotting, he or she will look for the cause of the condition by doing a physical exam.

Medical and family histories will also be reviewed in case you have a blood relative who has had the following:

  • Relatives with abnormal or excessive clotting
  • A history of repeated blood clots before age 40
  • Blood clots during pregnancy or while on birth control pills
  • Unexplained miscarriages
  • A history of excessive or unusual blood clots (such as in the veins in the liver or kidneys)

Blood work will also be reviewed. 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.

Your doctor may choose to do additional blood tests if more information is needed.

Written by American Heart Association editorial staff and reviewed by science and medicine advisers. See our editorial policies and staff.