A D-dimer test is a blood test that can be used to help rule out the presence of a serious blood clot.

The D-dimer test is most useful when your doctor thinks something else is causing your symptoms and wants to quickly rule out these causes:

• DVT, which may give you swelling, pain, or redness in your leg
• Pulmonary embolism, or PE, is a blood clot that has traveled to your lungs that may lead to trouble breathing, fast heartbeat, pain in your chest, and coughing.

In this case, the test is only helpful if you’re not too likely to have blood clots. A positive D-dimer test doesn’t mean you have a blood clot. Other tests will be needed to check for that. If your odds of having a clot are higher, you’ll need different tests. You have higher odds of a clot with:

• Antiphospholipid syndrome, a disease in your immune system
• Clotting diseases that you’re born with
• Major surgery, such as a knee replacement
• Major injury, such as a broken leg
• Long periods of sitting or lying down, such as a long plane ride or hospital stay
• Pregnancy or if you recently had a baby
• Some cancers