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Introduction ⬇

D-Dimer

D-dimers are produced as a degradation product of fibrin clots resulting from the action of three enzymes: (1) thrombin, due to activation of the coagulation cascade that converts fibrinogen into fibrin clots; (2) activated factor XIII, which cross-links fibrin clots; and (3) plasmin. The presence of D-dimer confirms that both thrombin generation and plasmin generation have occurred.

This test is used in the diagnosis of DIC and venous thromboembolism (VTE). The D-dimer test is more specific for DIC than are tests for FSPs. The test verifies in vivo fibrinolysis because D-dimers are produced only by the action of plasmin on cross-linked fibrin, not by the action of plasmin on unclotted fibrinogen.

Normal Findings ⬆ ⬇

Quantitative

<500 ng/mL D-dimer units

<0.5 mg/L fibrinogen equivalent units

Qualitative: No D-dimer fragments present

Procedure ⬆ ⬇

A venous blood sample of 5 mL is collected into a light blue–topped tube containing 3.2% sodium citrate and aprotinin. Label the specimen with the patient’s name, date and time of collection, and test(s) ordered. Place the specimen in a biohazard bag and return it to the laboratory 
immediately.

Clinical Implications ⬆ ⬇

  1. IncreasedD-dimer values are associated with:

    1. DIC (secondary fibrinolysis)

    2. Arterial thrombosis

    3. Kidney or liver failure

    4. VTE

    5. Late in pregnancy, preeclampsia

    6. MI

    7. Malignancy, inflammation, and severe infection

  2. D-dimer values are increased with tPA anticoagulant therapy.

Interventions ⬆ ⬇

Pretest Patient Care

  1. Explain test purpose and procedure.

  2. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

  1. Review test results; report and record findings. Modify the nursing care plan as needed. Counsel the patient regarding abnormal findings; explain the need for possible follow-up testing and treatment. Monitor for DIC and thrombosis.

  2. Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

Interfering Factors ⬆

  1. False-positive tests are obtained with high titers of RA.

  2. False-positive D-dimer levels increase as the tumor marker CA-125 for ovarian cancer increases.

  3. The D-dimer test will be positive in all patients after surgery or trauma.

  4. False-positive results found in estrogen therapy, normal pregnancy.