D-dimer cannot normally be detected in the blood or is present in very low concentrations, except in the case when the body itself creates (and breaks down) a clot. The clot consists of different parts of cross-linked fibrin, which gradually breaks down, and one of the final products of its breakdown is D-dimer.
Causes of elevated values
When a blood vessel or tissue is injured and begins to bleed, the body initiates the process of hemostasis to form a blood clot and stop the bleeding. Chains of proteins – fibrins – are formed, which cross-link with each other forming a fibrin network, which together with platelets helps keep the blood clot at the site of the injury until the injury heals.
There are a number of risk factors for the occurrence of elevated D-dimer values. Elevated values can be found: in the case of major surgical procedures, prolonged lying down (immobilization), use of contraceptive pills or hormone replacement therapy, fractures, pregnancy and recent childbirth, antiphospholipid syndrome, hereditary coagulation disorders (presence of factor V Leiden mutation, thrombophilia), previous venous thromboembolic events (VTE), obesity, smoking.
Symptoms of elevated values
Elevated D-dimer values most often occur in deep vein thrombosis (DVT), pulmonary embolism (PE) and disseminated intravascular coagulation (DIC). Symptoms of deep vein thrombosis are: leg pain, leg swelling, redness or red lines on the legs. Although blood clots most often form in the deep veins of the lower extremities, they can also form in other parts of the body.
Determination of D-dimer is important if the patient has any of the symptoms of pulmonary embolism: difficulty breathing, cough, coughing up blood, chest pain, rapid heartbeat.
Measuring D-dimer can also be helpful in the diagnosis of disseminated intravascular coagulation, a condition in which there is excessive activation and consumption of coagulation factors and the formation of thrombus throughout the body.
The main use of D-dimer as a laboratory-diagnostic parameter is to rule out the presence of thromboembolic disorders, primarily in the emergency diagnosis of patients with suspected deep vein thrombosis and pulmonary embolism. Increased D-dimer values are also expected in conditions such as disseminated intravascular coagulation, malignancy, sepsis, preeclampsia. High D-dimer values can also be found in other conditions such as some infections, liver diseases, some tumors. The values of this parameter increase during the years of life, so in people who are more than 80 years old, an increase in the value does not always have to be a sign of illness.
It is recommended that when D-dimer values are monitored during the course of the disease, the determination should always be performed in the same way, in the same laboratory.
Interpretation of results
A normal or “negative” D-dimer result (the D-dimer level is below predetermined thresholds) means that the person tested does not have an acute condition or disease that causes clots to form and break up. D-dimer determination is used to rule out clotting as a cause of symptoms.
A positive D dimer result indicates the possible presence of a blood clot (thrombus) in the body, but does not tell about its location or cause. However, increased values do not necessarily indicate the presence of thrombosis, as other conditions and factors can result in an increase in D-dimer levels (eg, in pregnancy, fibrin formation and breakdown also occur).
It is known that D-dimer is a test of high sensitivity – sensitivity, but low specificity, which means that it can be elevated in various conditions and diseases. It is used as an important additional parameter in laboratory diagnostics.
COVID-19 and elevated D-dimer levels
Since the beginning of the Covid-19 pandemic, the inclusion of D-dimer as a biomarker of prognosis and monitoring the course of this viremia has proven to be very useful. Elevated values of D-dimer and tendency to form blood clots have been observed in a certain number of patients.
With the infection of Covid-19, complications often occur, accompanied by thrombosis of veins and arteries in all parts of the body. It was found that the virus itself is able to initiate the coagulation process and thus lead to the formation of a thrombus. On the other hand, it is known that a strong inflammatory response of the body can damage blood vessels and start the process of thrombosis in them, and it manifests itself after long-term exhaustion, long lying down, blood composition disorders and increased viscosity due to high temperature and dehydration.
In patients with a more pronounced clinical picture, the Covid-19 virus, in addition to causing changes in the lungs, can significantly affect the venous and arterial system. Changes that can occur are cytokine storm, disruption of the coagulation cascade, and thrombotic complications. It has also been observed that complications are more common in people who already have problems with blood vessels, such as diabetics, people suffering from high blood pressure, some autoimmune diseases, and the like.
During the Covid-19 epidemic, numerous scientific studies were conducted that showed that there is a correlation between elevated D-dimer values and the severity of the disease. It has been confirmed that values that are very high (5 times higher than normal) in patients with Covid-19 have a higher chance of a bad outcome.
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If patients have elevated D-dimer values, it is necessary to introduce anticoagulant therapy – drugs that prevent the formation of thrombus.
If the patient does not come from an institution where he is already being treated, after talking with an Aqualab expert consultant, he is referred to Family Medica polyclinics and practices that work within this system.
Prof. Dr. Mirka Ilić
Specialist in medical biochemistry
Expert consultant of the Aqualab laboratory