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D-dimer (fibrinolytic activity)

Why is it needed?

D-dimer is a breakdown product of fibrin, which is formed during the dissolution of blood clots (fibrinolysis). The analysis is used for:
Diagnosis of thrombosis (PE, deep vein thrombosis).
✔ Elimination of thrombosis (at low level).
✔ Monitoring of anticoagulant treatment.
✔ Assessment of the risk of DIC (disseminated blood coagulation).

The role of D-dimer in the body

  1. Blood clot marker:
  • When a blood clot forms, fibrinolysis is activated – the process of destruction of fibrin.
  • D-dimer is a ‘fragment’ of broken fibrin, its level increases in the presence of a blood clot.
  1. Missing normally:
  • In a healthy body, the D-dimer is either undetectable or present in minimal amounts.

Symptoms of abnormalities

With an increased D-dimer (hypercoagulation)

  • Deep vein thrombosis (DVT):
  • Swelling, pain, and redness of the leg.
  • Pulmonary embolism (PE):
  • Shortness of breath, chest pain, hemoptysis.
  • DIC-syndrome:
  • Bleeding, multiple blood clots.
  • Pregnancy, cancer, COVID-19:
  • Moderate elevation without obvious symptoms.

With a reduced D-dimer

  • Normal condition (excludes active thrombosis).
  • Lack of fibrinolysis (rarely, with genetic disorders).

D-dimer norms in assays

It is measured in blood plasma (sodium citrate). References depend on the method:

MethodStandardPathology
ELISA (mcg / ml)< 0.5> 0.5 – risk of thrombosis
Quantitative (ng / ml)< 250–500> 500 – requires additional testing

Notes:

  • In pregnant women, the level increases (up to 1500 ng / ml in the third trimester).
  • Temporarily upgraded after operations/injuries .
  • In the elderly , the reference values are higher (up to 800 ng / ml).

When is the test scheduled?

  1. Suspected PE/DVT (combined with ultrasound, CT).
  2. Control of DIC syndrome.
  3. Monitoring of anticoagulant therapy (heparin, warfarin).

What should I do if I have an elevated D-dimer?

  1. Exclude thrombosis:
  • Ultrasound of the veins, CT angiography of the lungs.
  1. Anticoagulant therapy:
  • Heparin (unfractionated or low molecular weight).
  • Direct anticoagulants (apixaban, rivaroxaban).
  1. With DIC-syndrome:
  • Plasma transfusion, heparin.

Examples of interpretation

  • D-dimer = 1200 ng / ml + dyspnea → urgent CT scan to exclude PE.
  • D-dimer = 300 ng / ml → thrombosis is unlikely.

Conclusion

D-dimer is a key marker of fibrinolysis and thrombosis.
, The norm: < 500 ng / ml (method dependent).
🔹 Increase:

  • >500 ng / ml → look for thrombosis/DIC.
  • The references are higher for pregnant and elderly women.
    🔹 Low levels exclude active thrombosis.

Example: With a D-dimer of 50 ng/ml , thrombosis is unlikely, with 1500 ng/ml , an urgent diagnosis is needed.