D-dimers

D-dimers are breakdown products of fibrin, the protein mesh that holds a blood clot together. They only arise when fibrin has first been formed and then broken down again. The value thus describes the activity of clotting and clot dissolution throughout the body. They are measured in citrate plasma, which reaches the laboratory frozen; in the test catalogue they are listed together with troponin and NT-proBNP. The blood sample is taken in a practice and sent by express delivery.

How D-dimers arise in the body

When a blood vessel is injured, clotting begins: the enzyme thrombin converts fibrinogen dissolved in the blood into fibrin threads, and clotting factor XIII cross-links these threads firmly, so that a stable plug forms. As soon as the vessel is sealed, the body begins to dissolve the clot again (fibrinolysis). The enzyme plasmin cuts up the cross-linked fibrin, leaving fragments in which two so-called D domains are linked together – the D-dimers. They therefore indicate that clotting and dissolution are taking place in the body at the same time.

Low D-dimers – what does it mean?

A low D-dimer value is the normal case. It speaks against clots being formed and broken down on a larger scale at the time of the blood sample, and is therefore looked at to assess a fresh thrombosis or pulmonary embolism as less likely. With anticoagulant medicines, or when a clot has existed for some time, values can, however, be lower. A suddenly swollen, painful leg, chest pain when breathing in or sudden shortness of breath always require immediate medical attention.

Raised D-dimers – what happens in the body?

Raised D-dimers show that more fibrin is being formed and broken down in the body. This is the case with a thrombosis in the leg veins or a pulmonary embolism, but also after operations and injuries, with inflammation and infections, in pregnancy, with tumour diseases and with increasing age. Raised values alone therefore do not show where and why clotting is active. In COVID-19, studies have often observed raised D-dimers because the virus activates the inner lining of the blood vessels and the clotting system; whether lasting clotting changes after the infection are involved in long COVID symptoms is being investigated and is disputed.

The interpretation is given in your report.