D-dimer in the Diagnosis of Pulmonary Embolism

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D-dimer in the Diagnosis of Pulmonary Embolism

• Cheryl Pollock PGY-3

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Clinical Case

• 27 y.o. male
• Right anterior chest pain x 48h
• Pleuritic constant ache
• Mild non-productive cough, no hemoptysis
• Dyspnea on exertion
• No h/o trauma

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Physical Exam

• Vitals
• HR 76reg RR 18 T 37 BP 130/76
• CVS
• HS normal S1S2, no S3S4. No murmur.
• No leg swelling.
• Resp
• Normal breath sound intensity.
• Fine crackles R base.

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Diagnostic Testing

• Goal is to allow the clinician to revise the
  patients probability of having disease to a
  level greater than a treatment threshold or less
  than a test threshold

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Diagnostic Testing

• The cost of missing pulmonary embolism (PE) is
  high
• ED evaluation of patients with suspected PE is
  often complex, time-consuming
• D-dimer is increasingly used in the evaluation of
  suspected PE

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Do you want a D-dimer?

• Definition
• Conditions that cause a positive D-dimer
• Assays
• Its role in the work-up of pulmonary embolus
• Wells criteria
• Diagnostic algorithm

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D-dimer Defined

• Fibrin degradation product (FDP)
• Plasmin splits fibrin into fibrinogen and FDPs
• Fibrinolysis starts within 1h of thrombus
  formation
• T1/2 D-dimers 4-6 h
• Continued PE fibrinolysis elevated D-dimer
  levels for at least one week

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Positive D-dimer

• Venous thromboembolism
• DIC
• Acute coronary syndromes
• Vasculitis
• Malignancies lung, prostate, cervix, colon
• Vaso-occlusive sickle cell crisis
• Acute cerebrovascular accident
• Critically ill with severe infection, trauma,
  inflammatory disorders

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Positive D-dimer

• Many of these conditions are themselves risk
  factors for venous thromboembolism
• This complicates the interpretation of an
  abnormal value

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D-dimer Assays

• Five major types available
• Enzyme-linked immunosorbent assay (ELISA)
• Rapid ELISA
• Latex agglutination assay
• Whole blood assay
• Turbidimetric assay
• Immunofiltration assay

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ELISA Assay

• Positive if gt 500ng/ml
• In the diagnosis of PE
• Sensitivity 94-97
• Specificity 44
• Negative LR 0.07
• Drawback 2-4h to perform
• Rapid ELISA
• lt 2h
• Similar sensitivity and negative LR

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Interpretation of Results

• Estimation of the pretest probability is
  imperative for proper application of results
• Various methods
• Wells et al (Canada)
• Wicki et al (Switzerland)
• Kline et al (USA)
• The Wells criteria is used in this facility

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Wells Criteria
Criteria Points
Suspected DVT 3.0
Alternative Dx less likely 3.0
Heart rate gt100 bpm 1.5
Immobilization/surgery 1.5
Previous DVT/PE 1.5
Hemoptysis 1.0
Malignancy 1.0
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Wells Criteria Risk Interpretation
Score Probability of PE, with this score Risk
0-2 points 3.6 40 Low
3-6 points 20.5 53 Moderate
gt6 points 66.7 7 High
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Low Probability
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Moderate Probability
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High Probability
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Summary

• A normal D-dimer by an ELISA assay can safely
  exclude PE in patients with LOW to MODERATE
  pretest probability
• HIGH pretest probability V/Q scan
• D-dimer cant rule in PE
• In elderly or inpatients D-dimer usually
  abnormal- not useful

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Clinical Case

• Wells score
• No leg swelling, no pain
• HR lt100
• No immobilization
• No prior DVT or PE
• No hemoptysis
• No malignancy
• CXR RLL infiltrate
• Low pretest probability
• D-dimer negative

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The Simplest Algorithm

• You can safely rule out PE in pretest
  LOW-probablilty patients with a negative D-dimer

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Hamptons Hump
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High Probability VQ Scan
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EKG Findings