Lab

D-Dimer

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D-Dimer

  • 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
  • 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 [PubMed]
  • Labs
  • Measurement
  1. ELISA assay and advanced turbidimetric
    1. Most sensitive D-Dimer Assays
  2. Rapid latex agglutination
    1. First generation tests were variable
    2. Second generation tests appear to be adequate and similar to ELISA
  • Labs
  • Quantitative Assay Units
  1. Fibrinogen Equivalent Units (FEU)
    1. Newer measurement units that replace the older DDU
    2. FEU = 2 * DDU
    3. FEU Units are used for cutoffs described below
  2. D-Dimer Units (DDU)
    1. Older standard units replaced by the newer FEU
  • 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
  • Interpretation
  • Normal
  1. Negative Test: D-Dimer <400-500 ng/ml
  2. Discriminatory value in low risk Pulmonary Embolism
    1. Cutoff <500 ng/ml
      1. Adults at age <75 years
      2. First trimester pregnancy
      3. YEARS Score with any of 3 criteria present
    2. Cutoff <750 ng/ml
      1. Second trimester pregnancy
    3. Cutoff <1000 ng/ml
      1. Adults at age >75 years
      2. Third trimester pregnancy
      3. YEARS Score with all criteria absent
    4. ACP recommends Adult, age-adjusted D-Dimer cut-off
      1. Age >50 years old: Threshold = Age X 10 ng/ml
      2. Raja (2015) Ann Intern Med 163(9): 701-11 +PMID:26414967 [PubMed]
  3. References
    1. D-Dimer Cutoff of 1000 ng/ml in age over 80 years old has 100% Test Sensitivity
      1. Polo Friz (2014) Thromb Res 133(3): 380-3 [PubMed]
    2. Pregnancy related D-Dimer cutoffs
      1. Chan (2010) J Thromb Haemost 8(5): 1004-11 +PMID:20128870 [PubMed]
      2. Ercan (2014) J Matern Fetal Neonatal Med 25:1-5 +PMID:25060670 [PubMed]
      3. Kovac (2010) Eur J Obstet Gynecol Reprod Biol 148(1): 27-30 +PMID:19804940 [PubMed]
  • 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
  • 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 [PubMed]
    2. Lippi (2001) Clin Exp Med 1(3):161-4 [PubMed]
  • References
  1. Orman and Berg in Herbert (2015) EM:Rap 15(5): 10-11