A D-dimer test is a blood test that doctors can use to rule out a defective blood clot. This is helpful if your doctor suspects you have a blood clot in a lung or deep in a leg or pelvic vein.
These clots can be fatal. Prompt treatment increases your chances of survival and prevents other medical problems. Read on to learn more about the D-dimer test, how doctors use it, and its limitations.
What is D-Dimer?
D-dimer is a substance involved in the body's healing process. When you suffer an injury that causes bleeding, your body uses protein to store blood. The resulting clot clogs the damaged vessel.
Once the bleeding stops, your body sends out other proteins to slowly break down the clot. After that, the D-dimer fragments will remain in your blood.
These protein fragments tend to dissolve over time. However, if the clot does not break or otherwise form, you will have high levels of D-dimer in your blood.
The purpose of the test
The D-dimer test involves a simple blood draw. The healthcare professional will take a blood sample and analyze it with a fine needle. Results are ready in minutes.
Anyone can have a blood clot . Doctors often order a D-dimer test to rule out two dangerous types of blood clots.
Up to 100,000 people die each year in the United States from DVT and PE. Symptoms you may have include:
- Swelling or redness, usually in the lower leg, but sometimes in the thigh, pelvis, or arm.
- Leg, hip, pelvic, or arm pain.
- Difficulty breathing
- Fast heartbeat
- Chest pain
- Sweat a lot
Prompt treatment increases your chances of surviving PD and DVT. It will also help you avoid other medical problems that can affect your quality of life.
When is it useful?
Diagnosing these conditions can be challenging. One study found that nearly 70% of people with DVT symptoms treated in emergency departments were misdiagnosed.
In the past, doctors sent all blood samples to a central laboratory for analysis. This caused delays and meant that the test could not be used in an emergency. So doctors were forced to send patients for expensive imaging tests instead.
In recent years, the FDA has approved several rapid D-dimer tests. These tests provide doctors with a quick and inexpensive way to rule out DVT or PE.
interpretation of results
Results may vary depending on the test your doctor used and the design. Doctors need to know the normal and abnormal level ranges for the test they are using.
If your results are in the lower range, your doctor can safely rule out blood clots. If your results are abnormal or high, you will probably need more tests. A D-dimer test cannot be the sole basis for diagnosing DVT or PE.
Why the high D-dimer?
Many medical conditions, treatments, and lifestyle factors can increase D-dimer levels. This is why it's so important to answer your doctor's questions about your medical history in detail. People with blood clots often have one or more risk factors. They include:
Medical conditions and treatment:
- Heart disease : Patients with unstable angina or those who have had a heart attack have higher levels of D-dimer and an increased risk of blood clots in the future.
- Cancer : Certain cancers can increase your risk of blood clots.
- Cancer treatments : Chemotherapy and certain breast cancer drugs can increase the risk of blood clots.
- Estrogen treatment : Birth control pills and hormone replacement therapy can increase the risk of DVT and PE.
- Surgery : Patients who have undergone major surgery, such as hip or knee replacements, are at increased risk for blood clots. (Medications are prescribed to prevent this.)
- Infectious Diseases : COVID-19 and pneumonia can cause inflammation and blood clots.
- Kidney disease : For reasons that are not fully understood, kidney disease increases the risk of DVT and PE.
- Liver cirrhosis : People with severe liver disease are at increased risk of blood clots in a large vein in the liver.
- Pregnancy : At the time of delivery, the D-dimer level is two to four times higher. Women are at increased risk for DVT or PE for up to three months after delivery.
Other risk factors:
- Age : People over the age of 60 have a higher risk of blood clots.
- Smoking cigars
- Race : African Americans have higher levels of D-dimer than people of European descent.
- Gender : women have higher levels of D-dimer than men.
- A sedentary lifestyle : Lack of exercise or prolonged inactivity can increase the risk of DVT or PE. An example would be a long plane trip or a stay in the hospital.
Doctors will order other tests to make sure you don't have PE or DVT. These tests can include:
- Other blood tests – to see if you have a bleeding disorder.
- Ultrasonography : A test that uses high-frequency sound waves to take pictures of blood vessels, tissues, and organs.
- Ventilation-perfusion lung scan : A test that uses a radioactive substance to help doctors find out if air and blood can move through your lungs or if you have a blockage.
- CT angiography : A test in which a special dye is injected. Doctors use computed tomography to take high-definition images from different angles. The dye illuminates the blood vessels and tissues they need to detect blood clots.
Patients with a low risk for blood clots and low to moderate D-dimer levels probably do not have pulmonary embolism. Research shows that the D-dimer test is comparable to ultrasound or CT angiography in excluding PD.
If your test results are high, you will need more tests. Also, many people who have recently had PD will still have elevated levels of D-dimer. So the test will not help them.
deep vein thrombosis
Almost all patients with DVT have elevated levels of D-dimer. This makes the test useful to exclude the condition in patients with low to medium range levels. The test is also helpful if your symptoms are not so clear. If your level is high, your doctor will order additional tests.
Other medical conditions
Ruling out DVT and PE are the main reasons doctors order D-dimer tests. However, this test can help doctors evaluate and treat other serious conditions associated with blood clots. This includes:
- Coronary artery disease : People with severe heart disease have higher levels of D-dimer. People who are treated for a heart attack but still have high levels of D-dimer are at higher risk of having another heart attack or dying from it.
- Stroke : Higher levels of D-dimer are associated with an increased risk of stroke.
- Disseminated intravascular coagulation (DIC) : This is a rare condition in which blood clots form in blood vessels throughout the body. Elevated D-dimer levels are part of the DIC test.
- Hyperfibrinolysis : This blood clotting disorder is similar to disseminated intravascular coagulation syndrome. The D-dimer test also helps doctors evaluate the condition.
Doctors may order a D-dimer test if they suspect you may have a dangerous blood clot. The test helps doctors rule out two conditions that can be fatal: deep vein thrombosis, a blood clot in a vein and pulmonary embolism, a blood clot in the lung.
A negative test result means you probably don't have a blood clot. Usually no further testing is required. However, if your results are high again, this does not necessarily mean that you have a blood clot. The proof is not definitive. Your doctor will likely order other tests.
Get the word of drug information
Previously, doctors would send all patients suspected of having DVT or PE for imaging. It was expensive and time consuming. The D-dimer test is a quick and inexpensive blood test that can be used to rule out a dangerous blood clot. If your results are low, you probably have nothing to worry about.
However, many medical conditions, treatments, and lifestyle factors can increase D-dimer levels. Therefore, if your results are abnormal, you will need additional tests to confirm that you do not have a blood clot.
Frequently asked questions
Doctors prescribe this test to rule out the possibility of a serious blood clot. The two most commonly used conditions are pulmonary embolism, a blood clot in the lung, and deep vein thrombosis, a blood clot inside a vein, usually in the lower leg.
This is a simple blood test. Your healthcare provider will take a blood sample and analyze it with a fine needle.
You will get results in minutes.
If your results are low, you probably don't have a blood clot. If they go back up or are abnormal, it doesn't mean you have a blood clot. There may be other reasons for your results. Your doctor will need to order additional tests.