About the Test
Purpose of the test
D-dimer tests are used to help rule out the presence of an inappropriate blood clot (thrombus). Some of the conditions that the D-dimer test is used to help rule out include:
- Deep vein thrombosis (DVT)
- Pulmonary embolism (PE)
This test may be used to determine if further testing is necessary to help diagnose diseases and conditions that cause hypercoagulability, a tendency to clot inappropriately. A D-dimer level may also be used to help diagnose disseminated intravascular coagulation (DIC) and to monitor the effectiveness of DIC treatment.
What does the test measure?
D-dimer is one of the protein fragments produced when a blood clot gets dissolved in the body. It is normally undetectable or detectable at a very low level unless the body is forming and breaking down blood clots. Then, its level in the blood can significantly rise. This test detects D-dimer in the blood.
When a blood vessel or tissue is injured and begins to bleed, a process called hemostasis is initiated by the body to create a blood clot to limit and eventually stop the bleeding. This process produces threads of a protein called fibrin, which cross-link together to form a fibrin net. That net, together with platelets, helps hold the forming blood clot in place at the site of the injury until it heals.
Once the area has had time to heal and the clot is no longer needed, the body uses an enzyme called plasmin to break the clot (thrombus) into small pieces so that it can be removed. The fragments of the disintegrating fibrin in the clot are called fibrin degradation products (FDP), which consist of variously sized pieces of crosslinked fibrin.
One of the final FDP produced is D-dimer, which can be measured in a blood sample when present. The level of D-dimer in the blood can significantly rise when there is serious formation and breakdown of fibrin clots in the body.
If you are at low or intermediate risk for blood clotting (thrombosis) and/or thrombotic embolism, you can rely on the strength of the D-dimer test used in a hospital emergency room setting to determine the likelihood of a clot’s presence. A negative D-dimer test (below a predetermined cut-off threshold) indicates that it is highly unlikely that a thrombus is present.
But a positive D-dimer test cannot predict whether or not a clot is present. It indicates that further diagnostic procedures are required (e.g., ultrasound, CT angiography).
There are several factors and conditions associated with inappropriate blood clot formation. One of the most common is DVT, which involves clot formation in veins deep within the body, most frequently in the lower legs. These clots may grow very large and block blood flow in the legs, causing swelling, pain, and tissue damage.
It is possible for a piece of the clot to break off and travel to other parts of the body. This “embolus” can lodge in the lungs, causing a PE.
While clots most commonly form in the veins of the legs, they may also form in other areas as well. Measurements of D-dimer can be used to help detect clots in any of these sites. For example, clots in coronary arteries are the cause of myocardial infarction (heart attacks).
Clots may form on the lining of the heart or its valves, particularly when the heart is beating irregularly (atrial fibrillation) or when the valves are damaged. Also, clots can form in large arteries as a result of narrowing and damage from atherosclerosis. Pieces of such clots may break off and cause an embolus that blocks an artery in another organ, such as the brain (causing a stroke) or the kidneys.
Measurements of D-dimer may also be ordered, along with other tests, to help diagnose DIC, a condition in which clotting factors are activated and then used up throughout the body. This creates numerous tiny blood clots and at the same time leaves the affected person vulnerable to excessive bleeding.
DIC is a complex, sometimes life-threatening condition that can arise from a variety of situations, including some surgical procedures, sepsis, poisonous snake bites, liver disease, and the time after childbirth. Steps are taken to support the affected person while the underlying condition resolves. The D-dimer level will typically be very elevated in DIC.
When should I get this test?
D-dimer testing is often ordered when someone goes to the emergency room with symptoms of a serious condition such as chest pain and difficulty in breathing.
A D-dimer test may be ordered when someone has symptoms of DVT, such as:
- Leg pain or tenderness, usually in one leg
- Leg swelling, edema
- Discoloration of the leg
It may be ordered when someone has symptoms of PE such as:
- Sudden shortness of breath, labored breathing
- Coughing, hemoptysis (blood present in sputum)
- Lung-related chest pain
- Rapid heart rate
D-dimer is especially useful when a health care practitioner thinks that something other than DVT or PE is causing the symptoms. It is a quick, non-invasive way to help rule out abnormal or excess clotting as the underlying cause.
However, it should not be used when the probability of PE is high based on clinical assessment.
When a person has symptoms of DIC, such as bleeding gums, nausea, vomiting, severe muscle and abdominal pain, seizures, and decreased urine output, a D-dimer test may be ordered, along with a Prothrombin Time, Partial Thromboplastin Time, fibrinogen, and platelet count, to help diagnose the condition.
D-dimer may also be ordered at intervals when someone is undergoing treatment for DIC to help monitor its progress.
Finding a D-dimer Test
How can I get a D-dimer test?
A D-dimer test is most commonly ordered in a hospital. But it may be done as part of your regular testing regimen if you are monitoring the effectiveness of treatment for a blood clotting disorder like DIC. You can order a D-dimer test on your own at a laboratory without a doctor’s order, though if you’re monitoring conditions related to blood clotting, you need to be in consultation with a physician.
Can I take the test at home?
D-dimer tests are not available to do at home.
How much does the test cost?
Pricing for a D-dimer test varies depending on your health insurance and where the test is taken. The price and your coverage may also depend on if the test is done as part of a hospital visit to rule out a clot, versus whether you decide to order the test on your own.
With most insurance, diagnostic testing as part of an emergency room visit will be at least partially covered by your health insurance. Your best course of action is to check with your health care plan for information about costs, and if you’re responsible to pay a deductible or make copayments.
Taking a D-dimer Test
A D-dimer test is taken with a blood sample drawn from a vein in your arm.
Before the test
D-dimer tests do not require any special preparation before taking and you do not have to fast. It’s always good to ask your doctor or testing provider if there is anything they want you to do, though.
During the test
A D-dimer test is done like any other blood test. A phlebotomist will take your blood sample using a routine procedure called venipuncture. The tech will wrap an elastic band around your upper arm and may ask you to make a fist to get the blood flowing. Next, they’ll clean the area of the arm they are prepping with an alcohol wipe. They will then insert a needle to withdraw a vial of blood.
You may feel some slight pain and pressure when the needle goes in and comes out, but the whole thing is over in just a couple of minutes. When the tech removes the needle, they will apply some pressure and bandage your arm.
After the test
You should feel normal as soon as the test is complete other than a slight pain or bruising in your arm.
D-dimer Test Results
Receiving test results
If you’re getting a D-dimer test in a hospital emergency room, the hospital lab will work quickly to get results back in a couple of hours since time is of the essence. For more routine D-dimer tests that are done to monitor the effectiveness of ongoing treatments, you will typically get lab results in one to two days.
Interpreting test results
A normal or “negative” D-dimer result (with the level below a predetermined cut-off threshold) means that it is most likely that the person tested does not have an acute condition or disease causing abnormal clot formation and breakdown.
The units of a D-Dimer test may be provided in milligrams per liter (mg/L) fibrinogen equivalent units (FEU). According to the American Board of Internal Medicine, a negative D-dimer level is below 0.50 mg/L FEU, and it’s positive if it’s above 0.50 mg/L FEU.
Most health practitioners agree that a negative D-dimer is most valid and useful when the test is done if you are considered to be at low to moderate risk for thrombosis. The test is used to help rule out clotting as the cause of symptoms.
A positive D-dimer result may indicate the presence of an abnormally high level of fibrin degradation products. It indicates that there may be significant blood clot (thrombus) formation and breakdown in the body, but it does not tell the location or cause. For example, it may be due to a venous thromboembolism (VTE) or DIC. Typically, the D-dimer level is very elevated in DIC.
However, an elevated D-dimer does not always indicate the presence of a clot because a number of other factors can cause an increased level. Elevated levels may be seen in conditions in which fibrin is formed and then broken down, such as recent surgery, trauma, infection, heart attack, and some cancers or conditions in which fibrin is not cleared normally, such as liver disease.
Therefore, D-dimer is typically not used to rule out VTE in hospitalized patients (inpatient setting).
Fibrin is also formed and broken down during pregnancy, which may result in an elevated D-dimer level. But if DIC is suspected in a woman who is pregnant or is in the immediate postpartum period, then the D-dimer test may be used, along with a prothrombin time (PT), partial thromboplastin time (PTT), fibrinogen, and platelet count to help diagnose her condition. If the woman has DIC, her D-dimer level will be very elevated.
D-dimer is recommended as an adjunct test. Since D-dimer is a sensitive test but has a poor specificity, it should only be used to rule out DVT, not to confirm a diagnosis. It should not be used for PE when the clinical probability of that condition is high.
Both increased and normal D-dimer levels may require follow-up and can lead to further diagnostic testing. If you have positive D-dimer tests and moderate to high risk for DVT further study with diagnostic imaging (e.g., CT angiography) is required.
When used to monitor DIC treatment, decreasing levels indicate that treatment is effective while increasing levels may indicate that treatment is not working.
If you have questions about your D-dimer result, speak with your doctor. Some things you can ask include:
- How accurate is a D-dimer test?
- What are the next steps if I get a positive D-dimer result?
- Does a negative D-dimer mean I don’t have a DVT?
- Does an elevated D-dimer always mean that I could have a clot or some type of disorder?
- What if my D-dimer level is right around 0.50 mg/L FEU?
- National Blood Clot Alliance: Blood Clots in the United States
- American Society of Hematology: Blood Clots
- National Heart, Lung, and Blood Institute: What Is Venous Thromboembolism?
- National Heart, Lung, and Blood Institute: What Are Blood Clotting Disorders?
- Vascular Cures: What Is Vascular Disease?
- ClotCare: ClotCare Online Resource
- RadiologyInfo.org: Blood Clots