What a D-dimer test means during cancer care

This page is for people with cancer who have had a D-dimer blood test, or been told they need one. It explains what the test measures, what a high result can and cannot mean, and which symptoms need fast help.

Call 911 or go to the nearest emergency department if you have sudden trouble breathing, chest pain, or a fast heartbeat with fast breathing. A cough can also be a sign. MedlinePlus lists these as symptoms of a pulmonary embolism, a blockage in a lung artery, and says to get medical help right away. Do not wait for a clinic appointment.

Call your care team right away, day or night, if one leg becomes painful, tender, or swollen, or if the skin over it turns red, looks darker than usual, or feels warm. These are the symptoms MedlinePlus lists for deep vein thrombosis, a clot in a deep vein that usually forms in the lower legs. MedlinePlus says both leg clots and lung clots need quick medical treatment. If you cannot reach your care team, go to the nearest emergency department.

When a clot breaks down, it leaves debris behind. D-dimer is one piece of that debris. MedlinePlus describes it as a small piece of protein made when a blood clot dissolves in your body.

Here is the key detail. MedlinePlus says D-dimer is not usually found in your blood unless your body is making or breaking up blood clots. A higher than normal level may be a sign of a clotting disorder. That is what makes it worth measuring.

D-dimer helps answer "could there be a clot?" It does not tell you where a clot is, or how big.

MedlinePlus describes the test as a way to spot possible blood clots and decide whether more testing for a clotting problem is needed. It can also track how well treatment is working for conditions like DIC.

The conditions doctors use it to check for include:

• Deep vein thrombosis — a clot in a deep vein, usually in the lower legs
• Pulmonary embolism — a lung artery blockage, which MedlinePlus says usually happens when a clot elsewhere in the body breaks off and travels to the lungs
• DIC — clotting that happens too much throughout the body
• Stroke — caused by blocked blood flow to the brain

A negative result means low or normal D-dimer levels. MedlinePlus says this suggests you do not have a clotting problem. There is a catch, though: blood thinners can cause a false negative. If you take an anticoagulant, tell whoever orders the test.

A positive result means higher than normal levels, which may point to a clotting problem. It is not a diagnosis by itself. MedlinePlus is clear that more tests will be needed to show where a clot is or what type of clotting problem you have. Your provider may order imaging tests.

A flagged result on a portal can feel scary. A high number is not proof of a clot. Your team will look at your symptoms, your history and other test results together.

MedlinePlus lists other things, unrelated to clotting problems, that can raise D-dimer. These include pregnancy, heart disease, rheumatoid arthritis, and recent surgery. It adds that being older, or being unable to move around much, can also raise the level.

If you have had a recent operation, or you have mostly been in bed, those factors are on that list. So your team reads the number alongside everything else they know about you. They do not read it alone.

A D-dimer result is something to go through with your care team. What you can do is make sure your team has what they need:

• Tell them about any recent surgery, procedure, or long stretch of being immobile.
• List every blood thinner you take, including anything started recently.
• Describe your symptoms clearly: which leg, when it started, whether it gets worse standing up.

Keep the emergency guidance at the top of this page somewhere you can find it fast. Knowing exactly which symptoms mean "call now" removes a lot of the second-guessing that makes scary symptoms harder to act on.

• MedlinePlus — D-Dimer Test