D-dimer: The basics
D-dimer, a fibrin degradation product is a small protein fragment present in the blood after a blood clot is degraded by fibrinolysis. This protein is termed as D-dimer because it contains two D fragments of the fibrin protein joined by a cross-link.
Blood clotting is a crucial process that prevents excessive blood loss in case of an injury. Your body physiologically dissolves the clot once your injury has healed. However, in case of a blood clotting disorder, clots can form even when you do not have an injury, or they do not dissolve after healing of an injury. These conditions can be very serious and life-threatening and a D-dimer test can assess if you are suffering from one of these conditions. The D-dimer test has become highly important in COVID-19 pandemic as its elevated levels have been associated with disease severity and mortality trends. If you have been diagnosed or recovering from COVID and worried about how COVID impacted your health parameters, a D-dimer test can give valuable insights into it.
How is D-dimer produced?
When you get a cut, your body undergoes a sequence of steps to make your blood clump up. It is considered as a normal part of healing, as without a clot, you would keep bleeding and have much more blood loss. However, once the bleeding stops, you do not need the clot any longer as your blood flow gets hampered because of clotting. Thus, your body takes a series of steps in a different direction and breaks the clot down.
At the completion of all processes, D-dimer is the leftover product floating around in your blood and is detectable for up to eight hours after formation until the time the kidney clears it out. Thus, a dimer, a single fibrinogen molecule, is considered as one of the important proteins produced by the liver involved in the process of coagulation. In normal conditions, the levels of D-dimer are low whereas high levels of D-dimer in your blood indicates presence of a major clot.
Several studies suggest that levels of D-dimer may rise sharply in the case of COVID-19 and is associated with the severity of the disease.
What is the D-dimer test used for?
The test is also known as fragment D-dimer test or fibrin degradation fragment test.
D-dimer test is commonly used to assess a blood clotting disorder including:
- Deep vein thrombosis (DVT) : a blood clot situated deep inside a vein. Although these clots normally affect the lower legs, they can also occur in other parts of the body.
- Pulmonary embolism (PE) : defined as a blockage in an artery in the lungs. The most common cause of PE is loosening and travelling of a blood clot from another part of the body to the lungs.
- Disseminated intravascular coagulation (DIC) : a condition characterized with the formation of several blood clots that further results in organ damage and other serious complications. The most common causes of DIC are traumatic injuries, infections or cancer.
- Stroke : the blockage in the blood supply to the brain due to a clot in the arterial system of the brain vasculature.
How is the D-dimer test performed?
There is no special instruction for you to follow before undergoing this test. Your health care professional will take a blood sample from a vein in your arm, using a small needle. After the insertion of a needle, a small amount of blood will be collected into a vial. You will feel a little pinch or sting when the needle goes in or out of the skin.
What do the results normally mean?
Different labs may do the test differently, so the normal values of the test may differ. Your doctor can help you understand more clearly what your results mean.
● If the level of D-dimer is within normal limits, it means you probably don’t have a clotting disorder.
● If your levels of D-dimer are higher than normal value, you may have a clotting disorder such as PE, DVT, etc.
However, it cannot assess where the clot is located or what type of clotting disorder you have.
What does an elevated D-dimer in COVID-19 patients mean?
COVID-19 primarily causes lower respiratory tract infection presenting as cough, fever, dyspnea, and lethargy. However, few cases of the infection can progress into its severe forms like multi-organ failure, DIC, etc. Therefore, it is crucial to discriminate appropriately among infected patients, who are at higher risk of severe infection to treat them early for better prognosis. Raising D-dimer values can help identify people who can be at higher risk of COVID-19 complications.
Although the D-dimer test can rule out venous thromboembolism (VTE) in COVID-19 patients, an increased level of D-dimer does not necessarily mean that a patient has VTE. Due to low specificity of D-dimer test, it can be found in several other conditions, such as malignancy, trauma, liver disease, heart disease, sepsis, CPR or recent surgery. Therefore, take help of your doctor to decide your condition in the clinical context. Do not self-medicate or self-diagnose.
When and how often should D-dimer be measured?
There is no strict guideline as to how frequently D-dimer levels should be tested for management and/or monitoring of COVID-19 patients. Follow your doctor’s advice regarding health tests.
What is the outcome of increased D-dimer in a patient with COVID-19?
Various data suggests that D-dimer greater than 1 μg/ml is strongly associated with in-hospital death of COVID-19 patients.1
Similar findings are evident from other research that showed elevated D-dimer at admission and significantly, increasing D-dimer levels (3- to 4-fold over lab reference range) over time are related to poor outcomes such as increased clots, organ failure, etc.
In a nutshell
A higher level of D dimer in the body is indicative of presence of clot in the body which is regarded as a dangerous sign in patients with COVID-19. D-dimer in combination with other markers can also assist during the treatment of these patients, as the higher their D-dimer is, higher is the number of clots in the lung and the higher the chances of respiratory failure. Thus, D-Dimer test can be used to indirectly measure the severity of COVID-19 disease and assess its complications at an early stage.