What is a D-dimer test?
A D-dimer test is a blood test that measures D-dimer, which is a protein fragment that your body makes when a blood clot dissolves in your body. D-dimer is normally undetectable or only detectable at a very low level unless your body is forming and breaking down significant blood clots.
A positive or elevated D-dimer test result may indicate that you have a blood clotting condition, but it doesn’t guarantee that you have one. A D-dimer test can't reveal what type of clotting condition you have or where the clot is located in your body.
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How does blood clotting work?
Blood clotting, when functioning for its intended or normal purpose, is an important and essential process that prevents you from losing too much blood when you get injured. When a blood vessel or tissue in your body is injured and bleeds, your body kicks off a process called hemostasis to create a blood clot to limit blood loss and eventually stop the bleeding.
During the process of hemostasis, your body makes threads of a protein called fibrin, which weave together to form a fibrin net. The net, in addition to a type of cell called a platelet, helps anchor the forming blood clot in place until the injury heals. These blood clots may appear as scabs on your skin or bruises under your skin.
Once your injury has healed and your body no longer needs the blood clot, your body makes an enzyme called plasmin to break down the clot into small fragments in order to remove it. The fragments are known as fibrin degradation products, or fibrin split-products. D-dimer is one of those fibrin degradation products.
If you have a blood clotting condition, blood clots can form when you don’t have an injury, and/or they don’t break down when they should. In other words, your body’s blood clotting process isn’t working as it should. Blood clotting conditions can be serious and life-threatening.
Having a high D-dimer level in your blood can be a sign of a blood clotting disorder since the level of D-dimer can rise greatly when there’s significant formation and breakdown of blood clots in your body.
What is a D-dimer test used for?
Healthcare providers most often use D-dimer tests to help determine if someone has a blood clotting condition, which include:
- Deep vein thrombosis (DVT or venous thrombosis): Deep vein thrombosis is a blood clot that develops in a vein deep in your body. The clot may partially or completely block blood flow through the vein. Most DVTs happen in your lower leg, thigh or pelvis, but they can also occur in other parts of your body including your arm, brain, intestines, liver or kidney.
- Pulmonary embolism (PE): A pulmonary embolism is a blood clot in your lung that happens when a clot in another part of your body (often your leg or arm) flows through your bloodstream and becomes lodged in the blood vessels of your lung.
- Disseminated intravascular coagulation (DIC): DIC causes too many blood clots to form in your body, which can cause organ damage and other serious complications. In addition to using a D-dimer test to help diagnose DIC, healthcare providers use the test to help monitor the effectiveness of DIC treatment.
- Stroke: A stroke, or "brain attack," happens when a blood vessel in your brain becomes blocked or bursts.
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Why do I need a D-dimer test?
Your healthcare provider may have you undergo a D-dimer test if you’re having symptoms of a blood clotting condition, which include:
- Deep vein thrombosis (DVT).
- Pulmonary embolism (PE).
- Disseminated intravascular coagulation (DIC).
- Stroke.
Providers usually perform D-dimer tests in an emergency room or other hospital setting.
Deep vein thrombosis (DVT)
A DVT usually forms in one of your legs or arms. Not everyone with a DVT will have symptoms, but symptoms can include:
- Swelling of your leg or arm, which sometimes happens suddenly.
- Pain or tenderness in your leg, which may only happen when standing or walking.
- Warmth in the area of your leg or arm that’s swollen or hurts.
- Skin that is red or discolored.
- Having veins near the surface of your skin that are larger than normal.
If you’re experiencing signs and symptoms of DVT and aren't currently in a healthcare setting, call your healthcare provider as soon as possible.
Pulmonary embolism (PE)
Symptoms of a pulmonary embolism include:
- Sudden shortness of breath (dyspnea) or fast breathing.
- Sharp chest pain that often happens when you cough or move.
- Pain in your back.
- Coughing (sometimes with bloody spit or phlegm).
- Sweating more than you usually do.
- Fast heart rate (tachycardia).
- Feeling dizzy or fainting.
If you have symptoms of a pulmonary embolism, call 911 or get to the nearest emergency room as soon as possible.
Disseminated intravascular coagulation (DIC)
Symptoms of DIC include:
- Bleeding gums.
- Nausea and/or vomiting.
- Severe muscle pain and abdominal pain.
- Seizures.
- Peeing less than you normally do.
If you’ve already been diagnosed with DIC, your healthcare provider may have you undergo D-dimer tests regularly to make sure your treatment is working well.
Stroke
Symptoms of a stroke include:
- Sudden numbness or weakness in your face, arm or leg, especially on one side of your body.
- Sudden confusion, trouble speaking or difficulty comprehending what someone is saying.
- Sudden difficulty seeing in one or both of your eyes.
- Sudden trouble walking.
- Sudden dizziness, loss of balance or lack of coordination.
- Sudden severe headache with no known cause.
If you or someone else is experiencing these signs and symptoms of a stroke, call 911 or get to the nearest hospital as soon as possible.
Who performs a D-dimer test?
A healthcare provider known as a phlebotomist usually performs blood draws, including those for a D-dimer test, but any healthcare provider trained in drawing blood can perform this task. Your provider then sends the samples to a lab where a medical laboratory scientist prepares the samples and performs the tests on machines known as analyzers.
