D-dimers

Introduction

D-dimers are proteins that are formed when a thrombus is dissolved. They are cleavage products of fibrin that circulate freely in the blood. Their value is mainly determined when thrombosis is suspected.

However, its significance is limited. A high D-dimer value can have many causes and does not clearly prove the presence of a thrombosis. Conversely, a thrombosis can be ruled out with a high probability if the value is negative.

What are D-dimers?

Various substances are involved in blood coagulation. One of them is the protein fibrin, whose breakdown products can be measured in the blood. If a blood clot forms in the vascular system, it is dissolved within a short time.

Plasmin is responsible for its dissolution. It is an enzyme that splits fibrin and fibrinogen. The resulting fibrin cleavage products are then called D-dimers.

Causes for increased D-dimer values

The level of D-dimers in the blood can be elevated for a number of reasons. Most often it is determined to exclude a life-threatening pulmonary embolism. It is usually caused by deep vein thrombosis of the leg, in which the blood clot is released and enters the fine vessels of the lung with the blood.

In the case of disseminated intravascular coagulopathy (DIC), the value of the D-dimer is also outside the reference range. This is due to excessive consumption and subsequent lack of coagulation-promoting substances within the vessels. In connection with a cardiac event (e.g. heart attack), blood poisoning, tumor disease, liver cirrhosis, leukemia, pregnancy and after surgical interventions, an increase can also be observed.

Causes for permanently slightly increased D-dimer values can be very diverse. For this reason, no disease can be assigned to a positive test for D-dimers beyond doubt. Possible causes of such slightly increased values include pneumonia and COPD.

COPD is a disease of the lungs with permanently constricted airways. In addition, slightly elevated D-dimer values are also measured in numerous cancer diseases. Slightly elevated values are also caused by operations and injuries where tissue damage has occurred.

In addition, heart attacks, cirrhosis of the liver and renal insufficiency are also found. Severe inflammation, which leads to sepsis or to a hemolytic-uremic syndrome, can also be such a cause. Sepsis describes an unstable circulation as a result of an inflammation.

The hemolytic-uremic syndrome stands for a disintegration of red blood cells that are excreted through the kidney and damage it. In addition to these diseases, there are normal and healthy changes in the body as a result of menstruation, pregnancy or advancing age. In addition, there are many drugs that deliberately increase fibrin splitting and therefore also lead to an increase in the fibrin splitting products, namely the D-dimers.

In addition to these causes of a permanent slight increase in D-dimers, there are also diseases such as deep leg vein thrombosis or pulmonary embolism, which often show very high values for D-dimers. However, measurements taken at an early stage or when the disease is only mildly pronounced can also result in only slightly increased values in the blood. Among the most important drugs that increase D-dimer levels are those that deliberately increase fibrin cleavage.

These drugs are used to dissolve the blood clot in heart attacks, strokes, pulmonary embolism and deep vein thrombosis. They improve the blood flow and thus the oxygen supply to the affected areas of the body so that they suffer less damage. These drugs are uro- and streptokinase and recombinant tissue plasma activator, also known as rt-PA or alteplase.

In addition, there is the drug heparin, whose function is to counteract the formation of a blood clot. However, heparin therapy sometimes leads to the complication of “heparin-induced thrombocytopenia type 2″. Here, a general coagulation activity takes place, which leads to a consumption of platelets and also to an increase in the D-dimers in the blood.

In thrombosis, a blood clot forms within a vessel, which consequently hinders the uninterrupted flow of blood. The reason for its formation can be a disturbed balance of anticoagulant and coagulation-promoting factors, internal damage to the vessel walls or insufficient blood circulation after long immobilization. The value of D-dimers can only be assessed to a limited extent during pregnancy because changes in the female body cause a significant increase in cleavage products.

With the beginning of pregnancy the D-dimers increase continuously and reach their highest value in the last weeks before delivery. Accordingly, reference values for the D-dimers must be adjusted to exclude a thromboembolic event during pregnancy. The occurrence of thrombosis is one of the most frequent complications of pregnancy.

Overweight, long immobilization and regular vomiting promote the formation of a blood clot. In more than half of the cases, pregnancy thrombosis occurs before the 20th week. However, an increased risk remains until twelve weeks after delivery.