D-Dimer Test: Importance of D-dimer Test in Covid-19

D-dimer test is a simple blood test done to detect the presence of a blood clot.
D-dimer is one of the protein leftover substances floating around the blood when a blood clot dissolves in the body.

Generally it can not found or is found at a very low level. But, the levels of D-dimer rise if you have a major blood clot.

D-dimer is a protein fragment that called "Fibrin D- dimer" in the blood. Fibrin is the main component of blood clot which helps to reduce blood leak.

Blood clots generally start to slowly break down after they are formed, and this process releases D-dimer into the blood.

D-Dimer in COVID

When a blood vessel or tissue is injured and begins to bleed, a process called hemostasis is initiated by the body to create a blood clot to limit and eventually stop the bleeding.

⮞ This process produces threads of a protein called fibrin, which crosslink together to form a fibrin net. That net, together with platelets, helps hold the forming blood clot in place at the site of the injury until it heals.

D-Dimer Test

⮞ Once the area has had time to heal and the clot is no longer needed, the body uses an enzyme called plasmin to break the clot (thrombus) into small pieces so that it can be removed.

The fragments of the disintegrating fibrin in the clot are called fibrin degradation products (FDP), which consist of variously sized pieces of crosslinked fibrin. One of the final fibrin degradation products produced is D-dimer, which can be measured in a blood sample when present.

The level of D-dimer in the blood can significantly rise when there is significant formation and breakdown of fibrin clots in the body.

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Blood clots form whenever a blood vessel is damaged, whether that’s by an injury or by atherosclerosis, or when blood flow is restricted, such as by a vessel being compressed for a long time. D-dimer is normally undetectable in the blood but it is produced when the body is trying to break down a blood clot.

Blood clotting is an important process that prevents you from losing too much blood when you are injured.

D-Dimer Test

Normally, your body will dissolve the clot once your injury has healed. With a blood clotting disorder, clots can form when you don't have an obvious injury or don't dissolve when they should.

Why do I need this test?

Your doctor might ask you to have this test if they suspect you have blood clotting problems or wants to rule them out. You may need this test if your healthcare provider suspects you have a dangerous blood clot.

Pulmonary Embolism

It can damage part of the lung due to restricted blood flow, decrease oxygen levels in the blood, and affect other organs as well.

Your blood goes from your heart to your lungs through your pulmonary artery. In the lungs, the blood is supplied with oxygen, and then it goes back to the heart, which pumps the oxygen-rich blood to the rest of your body.

Pulmonary embolism symptoms incluide trouble breathing:

Cough
Chest pain
Rapid heartbeat

Deep vein thrombosis (DVT)

Blood clot (thrombosis) that forms in the deep veins located in the arm or leg. A blood clot (thrombus) in the deep venous system of the leg or arm, in itself, is not dangerous.

It becomes potentially life threatening when a piece of the blood clot breaks off and embolizes, travels through the circulation system through the heart, and enters into one of the pulmonary arteries and becomes lodged.

DVT

This can prevent blood from flowing properly through the lung and decreasing the amount of oxygen absorbed and distributed back to the body.
symptoms incluide Pain:

Swelling
Warmth
Redness
Leg cramps Leg pain or tenderness
Leg swelling
Redness or red streaks on the legs

Disseminated intravascular coagulation

DIC

Disseminated intravascular coagulation (DIC) is a rare but serious condition that causes abnormal blood clotting throughout the body's blood vessels.

It is caused by another disease or condition, such as an infection or injury, that makes the body's normal blood clotting process become overactive.
The underlying cause is usually due to inflammation, infection, or cancer.

In some cases of DIC, small blood clots form in the blood vessels. Some of these clots can clog the vessels and cut off the normal blood supply to organs such as the liver, brain, or kidneys.

What happens during a D-dimer test?

During this test health care professional will cleanse the area to be injected with an antiseptic and wrap an elastic band around the upper arm to make the vein visibleand pool with blood.

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

Will I need to do anything to prepare for the test?

You don't need any special preparations for a D-dimer test.

Are there any risks to a D-dimer test?

There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

What do the results mean?

⮞ If your result is "negative," you most likely don’t have a problem with blood clots, such as DVT.

⮞ If your result is "high," It means you’ll need more testing to see whether you have a blood clot. This test can’t confirm that you have DVT or PE. It can only help rule them out.

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

⮞ If result are normal (i.e. less than 500 nanograms/milliliter), It indicate that you are not affected.

⮞ If result are Abnormal (i.e. above than 500 nanograms/milliliter), It indicate that you are infected.

⮞ If your results show higher than normal levels of D-dimer, it may mean you have a clotting disorder.

D-Dimer

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 your D-dimer results were not normal, your provider will probably order more tests to make a diagnosis.

Doppler Ultrasound: A test that uses sound waves to create images of your veins.
CT angiography: In this test, you are injected with a special dye that helps your blood vessels show up on a special type of x-ray machine.
Pulmonary angiography
Ventilation-perfusion (V/Q) scan: These are two tests that may be done separately or together. They both use small amounts of radioactive substances to help a scanning machine see how well air and blood move through your lungs.