D-dimer in the Diagnosis of Pulmonary Embolism

1. D-dimer in the Diagnosis of Pulmonary Embolism Cheryl Pollock PGY-3

2. 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

3. 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.

4. Diagnostic Testing • Goal is to allow the clinician to revise the patient’s probability of having disease to a level greater than a treatment threshold or less than a test threshold

5. 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

6. 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

7. 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

8. 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

9. Positive D-dimer • Many of these conditions are themselves risk factors for venous thromboembolism • This complicates the interpretation of an abnormal value

10. D-dimer Assays • Five major types available: • Enzyme-linked immunosorbent assay (ELISA) • Rapid ELISA • Latex agglutination assay • Whole blood assay • Turbidimetric assay • Immunofiltration assay

11. ELISA Assay • Positive if > 500ng/ml • In the diagnosis of PE: • Sensitivity= 94-97% • Specificity= 44% • Negative LR = 0.07 • Drawback: 2-4h to perform • Rapid ELISA • < 2h • Similar sensitivity and negative LR

12. 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

13. Wells Criteria

14. Wells Criteria: Risk Interpretation

15. Low Probability

16. Moderate Probability

17. High Probability

18. 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 can’t “rule in” PE • In elderly or inpatients D-dimer usually abnormal- not useful

19. Clinical Case • Wells score • No leg swelling, no pain • HR <100 • No immobilization • No prior DVT or PE • No hemoptysis • No malignancy • CXR: RLL infiltrate • Low pretest probability • D-dimer = negative

20. The Simplest Algorithm • You can safely rule out PE in pretest LOW-probablilty patients with a negative D-dimer

21. Hampton’s Hump

22. High Probability VQ Scan

23. EKG Findings