D dimer test – An over view

D-dimer is a fibrin degradation product (or FDP), a protein fragment (small piece) that’s made when a blood clot dissolves in your body.. It also Known as Fragment D-dimer.

D-dimer concentration may be determined by a blood test to help diagnose thrombosis. Since its introduction, it has become an important test performed in patients with suspected thrombotic disorders. While a negative result practically rules out thrombosis, a positive result can indicate thrombosis but does not rule out other potential causes. Its main use, therefore, is to exclude thromboembolic disease where the probability is low. In addition, it is used in the diagnosis of the blood disorder disseminated intravascular coagulation. A four-fold increase in the protein is a strong predictor of mortality in those suffering from COVID-19.

A D-dimer test is most often used to find out whether you have a blood clotting disorder like

Deep vein thrombosis (DVT), a blood clot that’s deep inside a vein. These clots usually affect the lower legs, but they can also happen in other parts of the body.

Pulmonary embolism (PE), a blockage in an artery in the lungs. It usually happens when a blood clot in another part of the body breaks loose and travels to the lungs. DVT clots are a common cause of PE.

Disseminated intravascular coagulation (DIC), a condition that causes too many blood clots to form. They can form throughout the body, causing organ damage and other serious complications. DIC may be caused by traumatic injuries or certain types of infections or cancer.

Stroke, a blockage in the blood supply to the brain.

You may need this test if your healthcare provider suspects you have a dangerous blood clot. A blood clot that forms in a deep vein is called a deep vein thrombosis (DVT). A DVT is most commonly found in the legs. If the clot travels to the lungs, it’s called a pulmonary embolism (PE). In the lungs, the clot can cut off the flow of blood. This is a medical emergency and may cause death.

Symptoms of a blood clot include:

• Leg swelling (edema)
• Leg pain or tenderness
• Leg redness

If you have these symptoms, call your healthcare provider.

You may also have a D-dimer test if you have symptoms of a blood clot in the lungs, such as:

• Trouble breathing
• Coughing (may cough up blood)
• Fast heartbeat
• Chest pain 
• Sweating
• Fainting

People with blood clots often have one or more risk factors. These risk factors include:

Major surgery (for example, hip surgery) or injury (for example, a broken leg)

Not being able to move for long periods of time (for example, from being in the hospital, or taking long trips by plane or car)

Pregnancy or recent childbirth

Certain cancers

Antiphospholipid syndrome

Inherited clotting disorder, such as factor V Leiden mutation

You may also need this test to help diagnose and monitor treatment for other conditions.

If your results show low or normal D-dimer levels in the blood, it means you probably don’t have a clotting disorder.

If your results show higher than normal levels of D-dimer, it may mean you have a clotting disorder. But it cannot show where the clot is located or what type of clotting disorder you have. Also, high D-dimer levels are not always caused by clotting problems. Other conditions that can cause high D-dimer levels include pregnancy, heart disease, and recent surgery. If the D-dimer results were not normal, more tests might require for a diagnosis with the guidance of a qualified health care provider.

Positive readings can be due to various causes: liver disease, high rheumatoid factor, inflammation, malignancy, trauma, as well as advanced age.

False negative readings can occur if the sample is taken either too early after thrombus formation or if testing is delayed for several days. Additionally, the presence of anti-coagulation can render the test negative because it prevents thrombus extension. The anti-coagulation medications dabigatran and rivaroxaban decrease D-dimer levels but do not interfere with the D-dimer assay.

False values may be obtained if the specimen collection tube is not sufficiently filled (false low value if underfilled and false high value if overfilled). This is due to the dilutional effect of the anticoagulant (the blood must be collected in a 9:1 blood to anticoagulant ratio).

Likelihood ratios are derived from sensitivity and specificity to adjust pretest probability.

You may need more blood tests, including platelet count, fibrinogen, and prothrombin time. 

If your D-dimer test is positive, you will have other tests. You may have the following imaging tests to look for blood clots:

• Ultrasonography
• CT angiography
• Pulmonary angiography
• Ventilation/perfusion scanning 

These tests help your healthcare provider diagnose blood clots in your legs, arms, lungs, or other parts of the body.

A health care professional will take a blood sample from a vein, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial.

 

Source

https://en.wikipedia.org/wiki/D-dimer

https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=167&contentid=d_dimer

https://medlineplus.gov/lab-tests/d-dimer-test/

https://labtestsonline.org/tests/d-dimer#:~:text=D%2Ddimer%20tests%20are%20used,Pulmonary%20embolism%20(PE)