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What is D-dimer test?

D-dimer is a protein that is formed in the body due to the breakdown or fibrinolysis of blood clots. D-dimer levels are usually undetectable in the blood, but its levels start rising whenever there is an increased clot formation and dissolution. Thus, a D-dimer test helps in ruling out inappropriate clot formation (thrombus) in an intact blood vessel, which is seen in conditions such as deep vein thrombosis (DVT), pulmonary embolism (PE), stroke and even disseminated intravascular coagulation (DIC). This test also helps in determining the further need for diagnosis of hypercoagulability and monitoring the effectiveness of treatment in conditions such as DIC.

  1. Why is a D-dimer test performed?
  2. How do you prepare for a D-dimer test?
  3. How is a D-dimer test performed?
  4. What do D-dimer test results indicate?

A D-dimer test is usually performed in case of emergencies when there is a sudden onset symptom of chest pain, breathlessness or weakness in arms or legs. This test is also ordered when an individual shows apparent symptoms od DVT, PE or DIC. 

Symptoms of DVT include:

  • Leg pain, tenderness in one leg (affected leg)
  • Heavy pain in the affected area
  • Swelling of the affected leg (oedema)
  • Warm skin in the area of the clot
  • Discolouration of the affected leg

 Common PE symptoms are:

  • Sudden dyspnoea (breathlessness)
  • Cough
  • Haemoptysis (blood in the sputum)
  • Chest pain
  • Increased pulse rate (tachycardia)
  • Sudden collapse

DIC symptoms include:

More often than not, this test is done in conjunction with prothrombin time (PT), partial thromboplastin time (PTT) and platelet count for diagnosing DIC. A D-dimer test is also performed at regular intervals during DIC therapy to monitor the response to the treatment.

No special preparations are needed for this test.

It is a simple test that takes less than five minutes. An experienced laboratory specialist collects a blood sample from a vein in your arm by inserting a small needle into the vein. A small quantity of blood is withdrawn into a sterile vial or a test tube. A momentary pricking pain is felt when the needle goes in the vein.

There is a minimal risk of pain, light-headedness and bruising at the site of injection with the test. However, at most times, these symptoms disappear quickly. Rarely, an infection may occur at the site of withdrawal of blood.

Normal results: Absence of D-dimer in the blood or negative D-dimer results signify that there are no acute conditions or diseases that have led to the formation and breakdown of a clot and there is a low risk for thrombosis.

Abnormal results: Presence of D-dimer in blood indicate abnormally high fibrin breakdown, which hints towards the presence of a blood clot (thrombus) and its breakdown in the body. However, it cannot help in determining the location or reason for clot formation.

Positive D-dimer results can be seen in the following conditions:

For confirming the diagnosis as well as the location of DVT, VTE or PE, other diagnostic tests are performed along with the D dimer test. These include ultrasonography, computerised tomography (CT)-angiography, pulmonary angiography and ventilation-perfusion scanning.

A false positivity can be seen in certain normal conditions, such as pregnancy, or in patients aged above 80 years. In addition, D-dimers can show positivity in liver disease, high lipids or triglyceride levels, certain cancers, severe infections (sepsis), chronic heart disease or recent surgery or trauma.

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.

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References

  1. Kline JA. Evaluation of the pulmonary embolism rule out criteria (PERC rule) in children evaluated for suspected pulmonary embolism. Thromb Res. 2018 Aug;168:1-4. PMID: 29864629
  2. Leslie E. Silberstein, John Anastasi. Hematology: Basic Principles and Practice E-Book. Elsevier Health Sciences, 2017
  3. Eugene Braunwald, Douglas P. Zipes, Peter Libby. Heart Disease: A Textbook of Cardiovascular Medicine. Saunders, 2001
  4. Hamidreza Reihani et.al. Diagnostic Value of D-Dimer in Acute Myocardial Infarction Among Patients With Suspected Acute Coronary Syndrome. Cardiol Res. 2018 Feb; 9(1): 17–21. PMID: 29479381
  5. Hamidreza Reihani et.al. Diagnostic Value of D-Dimer in Acute Myocardial Infarction Among Patients With Suspected Acute Coronary Syndrome. Cardiol Res. 2018 Feb; 9(1): 17–21. PMID: 29479381
  6. Center for Disease Control and Prevention [internet], Atlanta (GA): US Department of Health and Human Services; Know the Risks, Signs & Symptoms of Blood Clots
  7. National Health Service [Internet]. UK; Deep vein thrombosis
  8. University of Rochester Medical Center. D-Dimer. Rochester, New York. [internet].