Type of test Blood

Normal findings

 < 250 ng/mL or < 0.4 mcg/Ml

 Test explanation and related physiology

 The fragment D-dimer test assesses both thrombin and plasmin activity. D-dimer is a fibrin degradation fragment that is made through lysis of crosslinked (D-dimerized) fibrin. As plasmin acts on the fibrin polymer clot, fibrin degradation products (FDPs) and D-dimer are produced. The D-dimer assay provides a highly specific measurement of the amount of fibrin degradation that occurs. Normal plasma does not have detectable amounts of fragment D-dimer. For discussion of other fibrin degradation products, see thrombosis indicators.

This test provides a simple and confirmatory test for disseminated intravascular coagulation (DIC). Positive results of the D-dimer assay correlate with positive results of other thrombosis indicators. The D-dimer assay may be more specific than the FDP assay, but it is less sensitive. Therefore combining the FDP and D-dimer assays provides a highly sensitive and specific test for recognizing DIC.

Levels of D-dimer can also increase when a fibrin clot is lysed by thrombolytic therapy. Thrombotic problems, such as deep vein thrombosis (DVT), pulmonary embolism (PE), sickle cell anemia, and thrombosis of malignancy, are associated with high D-dimer levels. D-dimer is used as an effective screening test for DVT. It is able to accurately identify patients with DVT who are then sent for venous duplex scanning . The D-dimer test, however, is often positive in patients who are already hospitalized. If the D-dimer test result is negative, its high predictability indicates that the patient does not have PE/DVT; further testing may not be necessary. D-dimer is an extremely sensitive and specific test for PE. Among patients presenting to the emergency department, normal D-dimer levels have a high negative predictive value for PE.

Finally, the D-dimer test can be used to determine the duration of anticoagulation therapy in patients with DVT. Patients with an abnormal D-dimer level 1 month after the discontinuation of anticoagulant therapy have a significant incidence of  recurrent DVT. This incidence can be reduced by restarting anti coagulation therapy.

 Interfering factors

• D-dimer level may be decreased in lipemic patients.

• The presence of rheumatoid factor at a level > 50 IU/mL may lead to increased D-dimer levels.

Procedure and patient care

 • See inside front cover for Routine Blood Testing.

 • Fasting: no

• Blood tube commonly used: blue

• Remember that if the patient is receiving anticoagulants or has coagulopathies, the bleeding time will be increased.

Abnormal findings

 Increased levels

- Fibrinolysis

-During thrombolytic or defibrination therapy with tissue plasminogen activator

- Deep vein thrombosis

- Pulmonary embolism

- Arterial thromboembolism

- Disseminated intravascular coagulation

- Sickle cell anemia with or without vasoocclusive crisis

- Pregnancy

- Malignancy

- Surgery