What is a D-dimer test?

D-dimer is a breakdown product produced by the normal process of clotting. It is normally present in small quantities in the blood; when increased it is suggestive of increased clotting activity in the body.

How is a D-dimer test performed?

D-dimer is a blood test, performed on the same tube as a coagulation profile or INR Test. It requires the tube to be filled to the correct level. A few millilitres of blood is taken from a vein.

When would you need a D-dimer?

A D-dimer is most commonly requested when the possibility of a deep venous thrombosis (DVT: a blood clot in the leg) or pulmonary embolism (PE: a blood clot in the lung) is being considered.

The test is used as risk-stratifying test, because it may make further testing unecessary in the correctly-selected patient. For example, a patient with a low risk of DVT or PE, with a negative (normal) D-Dimer test, will often not need to undergo further testing such as a Doppler Ultrasound of the legs or a CT Pulmonary Angiogram (CTPA).

The test is less useful at excluding clotting conditions in the body, when the clinical risk is moderate or high. The clinical probability, known as the pre-test probability, is based on a composite impression from the doctor, often incorporating specific items, which may have a points system assigned as a guide.

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D-dimer test results explained

D-dimer is one of the products of clot breakdown that can be measured in the bloodstream. Normally, this protein is present in small amounts because there is a constant turnover of tiny clots forming and being broken down by the body’s natural processes.

D-dimer may be NEGATIVE (normal):

Below a set cut-off value, determined by the laboratory and the brand of test, a small quantity of D-dimer in the blood is very reassuring, in the low-risk patient. It suggests that there is not much clot turnover in the body.

If the D-dimer is POSITIVE:

This may be due to non-specific inflammation, bedrest, after injury or surgery, and is more likely with increasing age. The majority of people with a positive d-dimer do not have a DVT or a PE; it simply means that these conditions cannot be excluded to a high degree of certainty.

The real value of a D-dimer test is in the low-risk patient, when the result is negative. Unfortunately it will more often be positive, and further testing will then usually be required to exclude a DVT or PE.

Related specialists

Related procedures

  • Blood Test (venesection)

Related tests

Also known as

  • D-Dimers
  • Fibrin Degradation Products (FDP)



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