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?
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.
- General Practitioner (GP)
- Emergency Physician
- General Physician
- Respiratory Physician
- Cardiothoracic Surgeon
- Orthopaedic Surgeon
- Blood Test (venesection)
- Coagulation Profile
- INR Test
- Platelet Count
- Chest X-Ray (CXR)
- Electrocardiogram (ECG)
- Legs Doppler Ultrasound Scan
- CT Pulmonary Angiogram (CTPA)
- VQ Scan (Ventilation-Perfusion Scan)
Also known as
- Fibrin Degradation Products (FDP)
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This article is for informational purposes only and should not be taken as medical advice. If in doubt, HealthEngine recommends consulting with a registered health practitioner.
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