D-dimer Test: What It Is and What It Shows

You have received a referral for a D-dimer blood test or are holding a form with a completed result. Let us calmly go over what this test shows, where the numbers come from, and in which cases additional examinations are needed.

What D-dimer is and what the test shows

D-dimer is a small protein fragment. It appears in the blood when a clot dissolves.

A healthy person has virtually none of this protein in their plasma. It arises only during active clot formation or breakdown.

The name "dimer" reflects its structure: the fragment consists of two D-parts of the fibrinogen molecule. The test measures the concentration of precisely these fragments.

The test does not show where a clot is located. It answers only the question of whether there has been an active clotting process.

Why a D-dimer blood test is ordered

The test is ordered when thrombosis is suspected. Most often this means deep vein thrombosis of the legs or pulmonary embolism.

Another indication is DIC syndrome. In this condition, too many clots form in the vessels, and they damage organs.

The test is also used to monitor treatment of clotting disorders. In DIC syndrome, it shows whether therapy is working.

A separate matter is COVID-19 infection. In hospitalized patients, a 4-fold rise in the marker is associated with a worse prognosis.

When the probability of thrombosis is low to moderate, a negative result almost rules out the diagnosis. The sensitivity of the method is 93–95%.

How blood is taken for D-dimer

Blood is drawn from a vein in the arm with a thin needle. The whole procedure takes less than five minutes.

No special preparation is needed: fasting before the test is not required.

Mild pain at the puncture site or a bruise is possible. This usually resolves quickly.

Laboratories use different analyzers and different antibodies. Therefore, reference values differ for each method.

What an elevated D-dimer means

A high level may indicate a clotting disorder. But by itself it does not confirm thrombosis.

The specificity of the test is about 50%. This means that an elevated marker is often present without thrombosis as well.

• pregnancy;
• recent surgery or trauma;
• inflammation, including high rheumatoid factor;
• cancer, liver disease;
• older age and immobility.

With a high result, the doctor usually orders imaging. This may be ultrasound of the leg veins, CT angiography, or lung scintigraphy.

Age is taken into account separately. After age 50, the threshold is recalculated: a value above age multiplied by 10 is considered abnormal.

What normal values of the marker mean

A normal or low D-dimer means that active clot formation and breakdown are most likely absent.

If the initial probability of thrombosis is not high, such a result reduces it to less than 1%.

A false-negative result can also occur. Its common cause is anticoagulants: they suppress clot growth.

Another cause is blood collection too early or too late after clot formation.

Therefore, a normal form does not cancel an examination. The doctor correlates the numbers with symptoms, history, and other tests.

When the result should be discussed with a doctor

Any result outside the laboratory's reference values requires a conversation with a doctor. Especially if symptoms are present.

Signs of deep vein thrombosis: throbbing pain in one leg, swelling, redness or darkening of the skin, enlarged veins.

Signs of pulmonary embolism: shortness of breath, cough, chest pain, rapid heartbeat and breathing. Some people have no symptoms at all.

A D-dimer abnormality by itself is not a reason to call an ambulance. Call 103 or 112 if pain and swelling of one leg are combined with shortness of breath or chest pain.

A planned conversation with a family doctor is needed if an elevated result was found incidentally. The doctor will decide whether a repeat test and imaging are required.

This material is for reference and does not replace a doctor's consultation.

This content is for reference and does not replace a doctor's consultation. Medical disclaimer