D-Dimer

Aka: D-Dimer

1. Indication
   1. Suspected Venous Thrombosis (DVT)
   2. Suspected Pulmonary Embolism (Low PE Probability)
      1. See Pulmonary Embolism Diagnosis
      2. Used in conjunction with non-invasive studies
      3. Reduces the need for angiography
   3. Consider using to risk stratify after Thromboembolism
      1. High D-Dimer at one month predicts recurrence
2. Efficacy
   1. Precautions
      1. Negative D-Dimer is reassuring if low probability
         1. Use more specific tests if suspicion is high
      2. Positive D-Dimer has minimal clinical value
         1. Positive does not raise DVT or PE Probability
   2. Test Sensitivity: 93% for Venous Thromboembolism
   3. Test Specificity: 25% for Venous Thromboembolism
   4. Negative Predictive Value: 99.5% if Low PE Probability
      1. Wells (2001) Ann Intern Med 135:98-107
   5. Measurement
      1. ELISA assay and advanced turbidimetric are most sensitive
      2. Rapid latex agglutination results may be variable
         1. Second generation tests appear to be adequate
3. Mechanism
   1. Marker for intravascular coagulation
   2. D-Dimer is degradation product of fibrin
   3. Indicates plasmin lysis of fibrin
   4. Presence of D-Dimer suggests thrombosis
4. Normal
   1. Negative Test: D-Dimer <400-500 ng/ml
   2. Consider using 1000 ng/ml as discriminatory value in low risk Pulmonary Embolism
5. Causes: Increased D-Dimer (not specific)
   1. Venous Thromboembolism (true positive)
      1. Pulmonary Embolism
      2. Deep Vein Thrombosis
   2. Other causes (false positives)
      1. Recent surgery (within prior 1 week)
      2. Myocardial Infarction
      3. Atrial Fibrillation
      4. Infection or Sepsis
      5. Cancer
      6. Concurrent systemic illness
      7. Oral Anticoagulant use
      8. Pregnancy
      9. Ongoing blood loss
      10. Decreased Renal Function
6. Disadvantages: Circumstances in which D-Dimer is not useful
   1. Concurrent Anticoagulant use
   2. Comorbid cancer
   3. Age over 70 years
   4. Post-surgical
   5. References
      1. Schutgens (2002) Am J Med 112:617-21
      2. Lippi (2001) Clin Exp Med 1(3):161-4