A D-dimer test is a blood test that helps your care team decide whether a dangerous blood clot might be present. It is one of the tools doctors use when they are worried about conditions like deep vein thrombosis (DVT) or a pulmonary embolism (PE). On its own it rarely gives a final answer, but it is very good at one thing: helping to safely rule clots out. Here is what the test measures, when it is ordered, and how to have it processed in the Ottawa area.
What D-dimer actually measures
D-dimer is a small protein fragment that is left behind when a blood clot forms and then starts to break down. Your body is constantly making and dissolving tiny clots as part of normal healing, so a little D-dimer in the blood is completely normal. When a larger or more significant clot forms and the body works to break it down, the level of D-dimer in your blood rises. Measuring that level gives your doctor a clue about how much clot activity is happening in your body right now.
When a D-dimer test is ordered
Doctors most often order a D-dimer when they are trying to rule out a blood clot in someone with suggestive symptoms. Common scenarios include a swollen, painful calf that could signal a DVT, or sudden shortness of breath and chest pain that could point to a PE. It may also be used to help assess suspected disseminated intravascular coagulation (DIC), a serious clotting disorder.
- Possible deep vein thrombosis (DVT): swelling, warmth, tenderness or redness, usually in one leg
- Possible pulmonary embolism (PE): sudden shortness of breath, chest pain, or a racing heartbeat
- Monitoring or investigation of certain clotting disorders when a physician orders it
Because a suspected DVT or PE can be an emergency, D-dimer is frequently drawn urgently in a hospital or emergency department, where results are needed quickly. It can also be ordered on an outpatient basis, for example when a physician is following up on a lower-risk concern and wants a requisition-based blood draw at a community lab.
Why a normal result is reassuring
The real strength of the D-dimer test is what a normal (negative) result tells you. In a person the doctor has already judged to be at low or moderate risk, a normal D-dimer makes a significant clot very unlikely. That can spare you from more invasive or higher-cost imaging, such as a CT scan or ultrasound. This is why the test is described as a good way to rule a clot out rather than to rule one in.
Why a high result is non-specific
A high D-dimer is harder to interpret. Many everyday situations raise the level without any dangerous clot being present, so an elevated result is a signal to investigate further, not a diagnosis. Your doctor will read it alongside your symptoms, your risk factors, and often follow-up imaging.
- Recent surgery, injury, or bruising
- Pregnancy and the weeks after giving birth
- Older age, which tends to raise baseline levels
- Infection, inflammation, or recent illness
- Some cancers and certain chronic conditions
Because of this, a raised D-dimer usually leads to a next step, most often an ultrasound of the leg for suspected DVT or a CT scan of the chest for suspected PE, rather than to treatment on its own.
How the test is done and where it is processed
A D-dimer needs only a routine blood sample from a vein in your arm, and no fasting is required. Your requisition will note if any other tests are being drawn at the same time. At Bio-Test Laboratory, samples are processed in our accredited facility, and coagulation results like D-dimer are typically available to your ordering provider quickly, with routine results generally released within 24 to 48 hours through our patient portal. If your symptoms are severe or came on suddenly, do not wait for an outpatient appointment; seek emergency care.
Getting your D-dimer test at Bio-Test
If your physician or nurse practitioner has ordered a D-dimer as outpatient follow-up, most bloodwork at Bio-Test is walk-in, first-come, first-served, with no appointment needed. Bring your valid Ontario health card and your requisition to any of our 11 locations across Ottawa-Carleton and Eastern Ontario. You can also book online through our patient portal, and home visits can be arranged by request for a fee. For a sudden, severe clot concern, go to the nearest emergency department instead.