D-Dimer

D-dimer is a byproduct of the breakdown of fibrin, the fibrous protein that makes up a significant portion of blood clots. Fibrinogen, a plasma glycoprotein precursor of fibrin, consists of three domains, two domains on the ends and one domain separating them in the middle. When fibrinogen is cleaved during the initiation of a clot, fibrinogen becomes fibrin, which forms an insoluble fibrous lattice that is subsequently cross linked and strengthened. The primary enzyme responsible for breaking down the fibrin clot (fibrinolysis) is called plasmin. When plasmin cleaves the cross linked fibrin polymer, several types of breakdown products are produced. One of these products is called D-Dimer, a protein containing two adjacent domains from fibrin. Since the domains in fibrinogen are not adjacent, D-dimer can only be produced from the breakdown of the cross-linked fibrin polymer. Thus D-dimer is not normally found in serum or plasma, but is present only if fibrinolysis has occurred and is therefore an excellent marker of the breakdown (and therefore the presence) of a blood clot. As such, the measurement of plasma or whole-blood D-dimer is a very useful test for diagnosing conditions which result from blood clots, especially those that are difficult to otherwise detect, and also in distinguishing conditions which have otherwise similar symptoms and clinical findings. Such conditions include pulmonary embolisms^2,3,4, deep vein thrombosis^5,6,7, disseminated intravascular coagulation^8,9, venous malformations¹⁰ and acute aortic dissection¹¹. D-dimer also seems to have a role in prognosis following a stroke, but the usefulness of D-dimer in this regard has been a matter of debate^12,13,14.

REFERENCES

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2. 2. Bounameaux, H., et. al. Measurement of D-Dimer in Plasma as Diagnostic Aid in Suspected Pulmonary Embolism. The Lancet, 337, 196-200, 1991.
3. 3. Ginsberg, J.S., et. al. Sensitivity and Specificity of a Rapid Whole-Blood Assay for D-Dimer in the Diagnosis of Pulmonary Embolism. Annals of Internal Medicine, 129, 1006-1011, 1998.
4. 4. Perrier, A., et. al. Diagnosing Pulmonary Embolism in Outpatients with Clinical Assessment, D-Dimer Measurement, Venous Ultrasound, and Helical Computed Tomography: A Multicenter Management Study. American Journal of Medicine, 116, 291-299, 2004.
5. 5. D'Angelo, A. et. al. Evaluation of a New Rapid Quantitative D-Dimer Assay in Patients with Clinically Suspected Deep Vein Thrombosis. Thrombosis and Haemostatis, 75, 412-416, 1996.
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7. 7. Wells, P.S., et. al. Does this Patient Have Deep Vein Thrombosis? JAMA, 295, 199-207, 2006.
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9. 9. Levi, M. Guidelines for the Diagnosis and Management of Disseminated Intravascular Coagulation. British Journal of Haemotology, 145, 24-33, 2009.
10. 10. Dompmartin, A., et. al. Elevated D-Dimer Level in the Differential Diagnosis of Venous Malformations. Archives of Dermatology, 145, 1239-1244, 2009.
11. 11. Ohlmann, P. et. al., Diagnostic and Prognostic Value of Circulating D-Dimers in Patients with Acute Aortic Dissection. Critical Care Medicine, 34, 1358-1364, 2006.
12. 12. Barber, M., et. al. D-Dimer Predicts Early Clinical Progression in Ischemic Stroke. Stroke, 37, 1113-1115, 2006.
13. 13. Welsh, P., et. al. Associations of Inflammatory and Haemostatic Biomarkers with Poor Outcome in Acute Ischaemic Stroke. Cerebrovascular Diseases, 27, 247-253, 2009.
14. 14. Haapaniemi, E. and Tatlisumak, T. Is D-Dimer Helpful in Evaluating Stroke Patients? A Systematic Review. Acta Neurologica Scandanavica, 119, 141-150, 2009.
15. 15. Lippi, G., et. al. Increased D-Dimer Value and Occult Cancer in the Absence of Detectable Thrombosis. Haematologica, 92, e53-e55, 2007.