What Is a D-Dimer Test?

The D-dimer test is a blood test that looks for the presence of D-dimer in your blood, which is a protein fragment and a by-product of a blood clot that breaks down or dissolves in your body. Your healthcare provider may order a D-dimer test if they suspect you have a blood clot.

This test requires a sample of your blood to measure D-dimer levels in your bloodstream. A phlebotomist (a health professional with training in drawing blood from the veins) will use a needle to remove a small amount of blood from a vein in your arm. Your blood sample will then go to a lab, where a medical laboratory scientist analyzes the sample to measure D-dimer levels. Once their analysis is complete, they send the results to your healthcare provider.

Purpose 

A D-dimer test helps healthcare providers diagnose blood clots or blood clotting disorders and monitor the effectiveness of blood clot treatments. The test detects the presence of D-dimer protein fragments in your bloodstream. High levels of D-dimer in your blood often indicate many smaller clots in one of your blood vessels.

D-dimer is a by-product of the body’s blood clot breakdown process. When you are injured and bleeding, your body sends proteins and platelets to the injury site to form a clot and stop the bleeding. Once the injury heals, your body creates enzymes to dissolve the clot, which release D-dimer protein fragments that circulate in your bloodstream as the clot dissolves.

Blood clotting disorders and other medical conditions can increase the risk of blood clots forming in your blood vessels. Blood clots in your legs (known as deep vein thrombosis) or lungs (known as pulmonary embolism) are potentially life-threatening and require prompt treatment.

While a D-dimer test is mostly used for diagnosing blood clots, this exam can also help monitor the effectiveness of blood clot treatments. For example, if your provider prescribes medication to help dissolve a blood clot, they may order a series of D-dimer tests to ensure the medicine is effective. D-dimer levels that steadily decrease indicate that the clot is dissolving and treatment is working properly.

How Does It Work? 

D-dimer tests are quick and simple blood tests that will take you, as the patient, less than five minutes to complete. Knowing what to expect ahead of time can help ensure a smooth experience and relieve any anxiety you have about the exam. 

Before the Test

A D-dimer test does not require special preparation. Unless your healthcare provider tells you otherwise, you can eat and drink normally before the test.

If your healthcare provider sends you to a lab for your blood draw, they may give you a bloodwork requisition (paperwork) similar to a prescription you’d take to a pharmacy. The requisition will have your name and birth date, the provider’s name and contact information, and the specific blood test (D-dimer) they are requesting.

During the Test 

The D-dimer test requires a blood draw to get your blood sample. A phlebotomist or other healthcare provider will perform the blood draw. This blood-drawing process involves the following steps:

• Step 1: Cleaning a small area on your arm with disinfectant where they will place the needle. In most cases, this is on the inside bend of your elbow. 
• Step 2: Wrapping an elastic band around your upper arm to make the veins in your lower arm swell with blood. 
• Step 3: Inserting a thin needle into a vein to draw a small amount of blood, which they can collect in a tube or vial attached to the needle. You might feel a slight pinch when the needle enters your vein.
• Step 4: Removing the band and needle from your arm and covering the area with gauze or a bandage to stop the bleeding. 

Once your blood draw is complete, your blood sample goes to the lab for analysis. 

After the Test

You can resume your normal activities after a D-dimer test. While the phlebotomist will only take a small amount of blood from your arm, it may be helpful to pack a healthy snack to eat on your way home, such as an apple, raisins, or almonds to ensure that a small loss of blood flow doesn't cause any symptoms—like dizziness or fatigue.

Risks and Precautions 

Like most blood tests, the D-dimer test is safe and low-risk. Some people may experience minimal side effects, such as minor discomfort and soreness in the arm, a small bruise at the site of the blood draw, and lightheadedness or nausea. If you feel woozy or dizzy during the blood draw, tell your healthcare provider.

How to Prepare for D-Dimer Test

The D-dimer test is quick and straightforward, but it can help to prepare ahead of time to help the process go smoothly.

Where To Go

The location of your D-dimer test will depend on your healthcare provider. If your healthcare provider has the necessary equipment, they may take a blood sample in their office. Or, they may send you to a laboratory, urgent care center, hospital, or diagnostic center, where a phlebotomist will take the blood sample.

What To Tell Your Provider

Tell your healthcare provider about your medications, including herbal supplements, vitamins, and over-the-counter drugs before you take the test. Some medications (e.g., anticoagulants) can affect D-dimer levels, and your healthcare provider will consider this when interpreting your test results.

What to Wear and Bring to the Test

It may be helpful to wear comfortable clothing, such as a t-shirt or a long-sleeve shirt with loose sleeves, so your arm is easily accessible for the blood draw. You may need to remove jewelry or accessories around your arm for the same reason.

When you arrive for your blood draw, bring your insurance card and any relevant paperwork, such as a requisition or referral form from your healthcare provider. You can bring a list of your current medications and medical history information if needed.

If you have a fear of needles or are concerned about feeling nauseous or dizzy during the blood draw, you can bring a friend or family member to your appointment for support. Depending on the facility’s policy, your loved one may be able to accompany you into the blood draw room to provide support.

How Much The Test Costs

Most health insurance plans cover the cost of the D-dimer test. Call your insurance provider or review your plan’s policy to know whether you will have out-of-pocket expenses, such as a copay. If you don’t have health insurance, talk to the testing facility about payment options. Some facilities may offer sliding scale payments based on your income.

Results

Your results should be ready within two days, depending on the lab. Some labs and healthcare providers have online patient portals to check the results yourself. Otherwise, the lab will send the results to your healthcare provider, who will call you or schedule an appointment to discuss your test results. 

Interpreting Your Results 

Your healthcare provider may call you to share your test results or schedule a follow-up visit to discuss your results, answer any questions you have, and determine the next steps. A normal D-dimer level is anything less than 0.50 milligrams per liter (mg/L).

• Positive results: Anything above 0.50 mg/L means you have elevated D-dimer levels and indicates the presence of a blood clot. The D-dimer test cannot indicate the location of a blood clot, so your healthcare provider may order additional diagnostic tests, such as an ultrasound, venography, or magnetic resonance imaging (MRI) test, to pinpoint its location.
• Negative result: A normal D-dimer level (0.50 mg/L or lower) usually indicates a low likelihood of a recent or current blood clot—but it doesn’t completely rule out the possibility. This is especially true if you have symptoms of or risk factors for blood clots (e.g., diabetes, obesity, or recent surgery). Your healthcare provider may also order additional tests to confirm the results of your D-dimer test.

Inaccurate Results 

The results of most d-dimer tests are accurate, but inaccuracies can sometimes occur due to variations in testing methods, medications, or underlying conditions. In rare cases, you might receive one of the following results:

• False positive result: A false positive occurs when you have elevated D-dimer levels in your blood but do not have a blood clot. Certain conditions can elevate D-dimer levels without a clot, including pregnancy, a recent infection or surgery, rheumatoid arthritis, lupus, and sickle cell disease. Certain medications that contain estrogen can also lead to false positives, including hormone replacement therapy or birth control pills.
• False negative result: A false negative test occurs when you have a blood clot, but your D-dimer test results do not reflect the presence of a clot. This can happen if the test occurs as a new clot forms or if you take anticoagulant medications.

When you have an inaccurate test, your healthcare provider may recommend doing a second D-dimer test or using other diagnostic measures to identify the presence of any blood clots in your body.

A Quick Review 

The D-dimer test is a simple blood test that measures the levels of D-dimer protein fragments in your blood. Elevated D-dimer levels can determine the presence of a blood clot in your body. Blood clots in your leg (deep vein thrombosis) and lung (pulmonary embolism) are potentially life-threatening and require prompt treatment. While the D-dimer test does not offer a definitive diagnosis, it’s an important tool in detecting and managing blood clots.