D-dimers: what are they exactly?
Before explaining what d-dimers are, we must talk about the mechanism of coagulation. When a blood vessel is damaged (in the event of external or internal bleeding), a coagulation process takes place: several proteins synthesized by the liver – called “coagulation factors” – work together to formation of a blood clot to stop the flow of blood.
Thus, several coagulation factors react to produce thrombin; thrombin converts fibrinogen into fibrin; the fibrin divides into small filaments that bind together (like a net) to plug the vascular breach. Finally, this clot is stabilized by factor XIII – another coagulation protein – and stays in place for 10 to 14 days, while it heals.
Problem: sometimes “abnormal” blood clots form in the veins and arteries. The body then tries to destroy these local clots which could “block” the blood flow and cause phlebitis (clot in a vein) or arterial thrombosis (clot in an artery). The destruction of a blood clot leads to the production of specific waste, resulting from the degradation of fibrin: these are the d-dimers.
D-dimers: in which cases do we dose them?
The blood test for d-dimers is not a “routine” examination that is commonly done in the laboratory: it is specifically prescribed by the doctor in case of suspected thrombotic disease (a pulmonary embolism, for example).
The blood dosage of d-dimers involves a simple blood test, without any special precautions: it is not necessary to be fasting for the sample. ” It is an examination that can be done urgently (in the laboratory or in the hospital) with results that can be obtained in less than 4 hours “underlines Pierre Zachary, biologist in Strasbourg (67).
To know. If the “normal” blood level of d-dimers varies with age and sex, the upper limit is 500 micrograms per liter of blood (μg / L). It should be noted that the results of the blood test may be falsified in the event of anticoagulant treatment, inflammatory syndrome or even in the event of rheumatoid arthritis.
D-dimers: how to interpret a rate that is too high?
An abnormally high blood concentration of d-dimers (that is to say: greater than 500 μg / L) is an “alarm bell” which should immediately suggest a thrombotic disease. An excess of d-dimers in the blood may thus reflect:
- A phlebitis. Phlebitis (also called “venous thrombosis”) corresponds to the obstruction of a vein, most often in the lower limbs, following the formation of a blood clot (thrombus). It manifests as pain, a feeling of warmth and swelling in the affected limb – often it is a calf. When phlebitis forms in a superficial vein, it is benign (we then speak of paraphlebitis or periphlebitis); when it forms in a deep vein, it can progress to pulmonary embolism.
- Pulmonary embolism. Pulmonary embolism is a complication of phlebitis: it corresponds to the migration of the blood clot (thrombus) formed in the veins of the lower limbs to the pulmonary arterial circulation. This is a medical emergency which results in shortness of breath (dyspnea), rapid heartbeat (tachycardia), chest pain, irritating cough and / or bloody cough.
- Disseminated intravascular coagulation (DIC). Disseminated intravascular coagulation (also called consumer coagulopathy or defibrination syndrome) is a disease that corresponds to a pathological activation of coagulation – on the symptom side, it results in the formation of multiple clots in the bloodstream.
- Physical trauma. For example: a fall, a muscle crush …
And also… An abnormal rise in d-dimer levels may also be seen in liver, heart or kidney disease, but also in cancer. In addition, as Pierre Zachary explains, ” the blood level of d-dimers is naturally higher in pregnant women, so this test is not relevant during pregnancy “.
To know. ” An abnormally high blood level of d-dimers is not sufficient for a diagnosis and instead opens the way for further testing – for example, ultrasound “emphasizes the biologist.
Thanks to Pierre Zachary, biologist at Biogroup in Strasbourg (67).
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