by Dr. Adele Visser
Introduction
D-dimer is a by-product which forms from fibrin during coagulation. In the clinical setting, it is broadly used in the exclusion of venous thrombosis.
However, more recently, its use has been extended to a range of conditions, where it is of prognostic value (cardiovascular disease and malignancy) and even more recently, in the use of COVID-19 disease1.
Clinical uses of D-dimer
As per the American Society of Hematology (ASH) guidelines, the D-dimer assay should be used within the correct clinical setting to allow for appropriate interpretation of quantitation.
Pulmonary embolism2
Patients should be stratified according to their risk probability for a pulmonary embolism.
In patients within the low probability subsection, a D-dimer can be used as a rule-out test. If equivocal or elevated, a VQ or CTPA should be performed.
Patients with a high pre-test probability requires CTPA or VQ scans. There is no indication to perform a d-dimer following either of these visualization studies.
Lower extremity Deep Vein Thrombosis (DVT)
Patients should be stratified according to their risk probability for a deep vein thrombosis. In patients within the low probability subsection, a D-dimer can be used as a rule-out test. If equivocal or elevated, a lower extremity ultrasound or whole-leg ultrasound should be performed.
Patients with an intermediate pre-test probability (25%), requires serial proximal leg ultrasound, whereas patients with a high pre-test probability (>50%) requires whole-leg ultrasound – serial testing indicated if uncertainty remains.
Upper extremity DVT
Patients should be stratified according to their risk probability for an upper extremity DVT. In patients within the low probability subsection, a D-dimer can be used as a rule-out test, followed by a duplex ultrasound as confirmation. Patients with a high pre-test probability requires serial duplex ultrasound. D-dimer should never be used in isolation in the diagnosis of an upper extremity DVT.
COVID-19 disease3
D-dimer can be reliably utilized as a prognostic marker in COVID-19 disease with values exceeding 2,14mg/L having a higher association with mortality in this setting.
Disseminated Intravascular Coagulation (DIC)4
In addition to the platelet count, aPTT and fibrinogen, the D-dimer is used in a scoring system for the diagnosis of DIC. Values are scored in reference to multiples of the upper limit of normal.
References
- Schutgens RE. 2020. D-dimer in COVID-19: A Guide with Pitfalls. Hemasphere. Aug; 4(4):e422
- Lim, W., et al. 2018. American Society of Hematology 2018 guidelines for management of venous thromboembolism: diagnosis of venous thromboembolism. Blood advances, 2(22), pp.3226-3256.
- Yao, Y., et al. 2020. D-dimer as a biomarker for disease severity and mortality in COVID-19 patients: a case control study. Journal of Intensive Care. 8(49)
- Levi, M., 2018. How I treat disseminated intravascular coagulation. Blood. 131(8):845-854.