D-dimer (or D dimer) is a fibrin degradation product (or FDP), a small protein fragment present in the blood after a blood clot is degraded by fibrinolysis. It is so named because it contains two crosslinked D fragments of the fibrin protein.

D-dimer concentration may be determined by a blood test to help diagnose thrombosis. Since its introduction in the 1990s, it has become an important test performed in patients with suspected thrombotic disorders. While a negative result practically rules out thrombosis, a positive result can indicate thrombosis but does not rule out other potential causes. Its main use, therefore, is to exclude thromboembolic disease where the probability is low. In addition, it is used in the diagnosis of the blood disorder disseminated intravascular coagulation.


Dabigatran is an oral anticoagulant from the class of the direct thrombin inhibitors. It is being studied for various clinical indications and in some cases it offers an alternative to warfarin as the preferred orally administered anticoagulant (“blood thinner”) since it does not require blood tests for international normalized ratio (INR) monitoring while offering similar results in terms of efficacy.

Deep Vein Thrombosis

Deep vein thrombosis, or deep venous thrombosis, (DVT) is the formation of a blood clot (thrombus) within a deep vein, predominantly in the legs. Non-specific signs may include pain, swelling, redness, warmness, and engorgedsuperficial veins. Pulmonary embolism, a potentially life-threatening complication, is caused by the detachment (embolization) of a clot that travels to the lungs. Together, DVT and pulmonary embolism constitute a single disease process known as venous thromboembolism. Post-thrombotic syndrome, another complication, significantly contributes to the health-care cost of DVT. Prevention options for at-risk individuals include early and frequent walking, calf exercises, anticoagulants, aspirin, graduated compression stockings, and intermittent pneumatic compression.

In 1856, German pathologist Rudolf Virchow postulated the interplay of three processes resulting in venous thrombosis, now known as Virchow’s triad: a decreased blood flow rate (venous stasis), increased tendency to clot (hypercoagulability), and changes to the blood vessel wall. DVT formation typically begins inside the valves of the calfveins, where the blood is relatively oxygen deprived, which activates certain biochemical pathways. Several medical conditions increase the risk for DVT, including cancer, trauma, and antiphospholipid syndrome. Other risk factors include older age, surgery, immobilization (as with bed rest, orthopedic casts, and sitting on long flights), combined oral contraceptives, pregnancy, the postnatal period, and genetic factors such as a non-O blood type. The frequency of occurrence (incidence) increases dramatically from childhood to old age; in adulthood, about 1 in 1000 adults develops DVT annually.

Individuals suspected of having DVT may be assessed using a clinical prediction rule such as the Wells score. A D-dimertest may also be used to assist with excluding the diagnosis (because of its high sensitivity) or to signal a need for further testing. Diagnosis is most commonly done with ultrasound of the suspected veins. Anticoagulation is the standard treatment; typical medications include a low-molecular-weight heparin and a vitamin K antagonist. Wearing graduated compression stockings appears to reduce the risk of post-thrombotic syndrome.


Dicoumarol is a naturally occurring anticoagulant that functions as a functional vitamin K depleter (similar to warfarin, a drug that dicoumarol inspired). It is also used in biochemical experiments as an inhibitor of reductases.

Dicoumarol is a natural chemical substance of combined plant and fungal origin. It is a derivative of coumarin, a substance that does not itself affect coagulation, but which is transformed into active dicoumarol. Dicoumarol does affect coagulation.

Direct thrombin inhibitors

Direct thrombin inhibitors (DTIs) are a class of medication that act as anticoagulants (delaying blood clotting) by directly inhibiting the enzyme thrombin (factor II). Some are in clinical use, while others are undergoing clinical development. Several members of the class are expected to replace heparin (and derivatives) and warfarin in various clinical scenarios.

Disseminated intravascular coagulation

Disseminated intravascular coagulation (DIC), also known as disseminated intravascular coagulopathy or less commonly as consumptive coagulopathy, is a pathological process characterized by the widespread activation of the clotting cascade that results in the formation of blood clots in the small blood vessels throughout the body. This leads to compromise of tissue blood flow and can ultimately lead to multiple organ damage. In addition, as the coagulation process consumes clotting factors and platelets, normal clotting is disrupted and severe bleeding can occur from various sites. DIC does not occur by itself but only as a complicating factor from another underlying condition, usually in those with a critical illness. The combination of widespread tissue ischemia and simultaneous bleeding carry an increased risk of death in addition to that posed by the underlying disease. DIC can be overt and severe in some cases, but milder and insidious in others. The diagnosis of DIC depends on the findings of characteristic laboratory tests and clinical background. Treatment is mainly geared towards the underlying condition.