The Clinical Utility of D-dimer Assays

1. The Clinical Utility ofD-dimer Assays • Beth Phillips MT,SH (ASCP) • Zone Technical Application Specialist • Siemens Healthcare Diagnostics

2. Objectives: • Define VTE as DVT and PE • Identify D-dimer assays and the role they play in DVT/PE • Explain Well’s pre-test probability scoring and clinical models • Describe evaluation of D-dimer assay results

3. History of Fibrinolysis • 4th Century BC…Hippocratic school familiar with blood fluidity • 1687 (300 years later) Malpighi noted blood clotted & reliquidfied after death • 1893 Dastre coined term “fibrinolysis” • 1905 Morawitz concluded process was probably enzymatic • 1959 Sherry proved fibrinolysis due to activator converting plasminogen to plasmin • 1960 five fragments of fibrinogen when treated with plasmin: A, B, C, D, & E • 1983 Greenberg measured “fibrin d-dimer” to differential FDP derived from fibrinogen or fibrin

4. Use of D-Dimer • 30 years ago proposed as aid in suspect DVT • mid 1990’s focus on use as aid in ruling out VTE • DIC profile

5. Venous Thromboembolism Epidemiology • Yearly in the USA: • > 600,000 Deep Vein Thrombosis • ~ 150,000 Pulmonary Embolism • Diagnostic Challenges with DVT/PE • 90% of PE develop from DVT • PE mortality 18%-30% without treatment • VTE suspected…..15% - 25% actually positive • Clinical suspicion has increased • Prevalence has decreased, some statistics state only 10% of suspected VTE are positive

6. Embolus Venous Blood Clot VENOUS THROMBOEMBOLISM • Venous Thromboembolic Disease • DVT • PE • Distinct clinical entities • Manifestation of the same disease

7. VENOUS THROMBOEMBOLISM • DVT-- thrombi form in deep veins of legs, pelvis or upper extremities • PE -- thrombi embolize to pulmonary arteries • elevate pulmonary vascular resistance • heart failure • cardiogenic shock • impairment of gas exchange

8. Deep Vein Thrombosis (DVT) • DVT may occur without obvious symptoms and may be difficult to detect • Up to 50% of DVT incidents may produce minimal symptoms or are completely "silent” • 85% are in the proximal venous system and 15% limited to the calf • 20% to 30% of calf thrombi extend proximally • Symptoms: • Pain, tenderness, or sudden swelling in the leg • Discoloration or visibly large veins • Skin that is warm to the touch

9. Pulmonary Embolism (PE) • The highest incidence of recognized pulmonary embolism occurs in hospitalized patients • Approximately 10% of patients with diagnosed pulmonary embolism die within the first 60 minutes • Symptoms: • Shortness of breath • Anxiety or nervousness • Rapid pulse • Excessive sweating • Sharp chest pain • Cough that may produce a bloody discharge • Very low blood pressure • Fainting

10. WHY IDENTIFY PATIENTS WITH VTE • Prevent mortality and morbidity associated with PE • Anticoagulant therapy reduces risk of fatal outcome 15 fold • Anticoagulant therapy related to high mortality and morbidity • Justification for risk of bleeding • Cost savings

11. VTE Disease Predisposing Risk Factors • Clinical conditions • surgery, trauma, cancer • hormonal influences • Hereditary coagulapathies • Factor V Leiden • Protein C / S Deficiency • AT Deficiency • Prothrombin Gene Mutation • Acquired coagulapathies • Lupus Anticoagulant • Environment • air travel • smoking • age

12. Diagnostic Challenges with DVT/PE • Only 15-25% of suspected VTE patients have disease • DVT mortality rate of 21% in elderly • PE mortality rate 30% without treatment • 90% of PE develops from DVT • PE causes more deaths annually in the U.S. than breast cancer, highway fatalities and AIDS combined

13. DIAGNOSING DVT/PE Determines Clinical Probability History and Exam Low Moderate High Guides Choice Diagnostic Studies

14. D-Dimer + Probability Score “…DD testing has gained wide acceptance for ruling out the disease, at least in the outpatient population referred to the emergency department.” “…ELISA DD assays and automated latex turbidimetric tests are associated with the highest sensitivity and with virtually no interobserver variability.” “…these tests should be used to rule out VTE only in non-high clinical probability patients.” D-Dimer for venous thromboembolism diagnosis: 20 years later; M. Righini, A. Perrier, P. De Mperloose amnd H. Bpima,eaix Journal of Thrombosis and Haemostasis, 2008, 6: 1059-1071

15. Wells Pre-test Probability of DVT Clinical Parameter Score Score Active cancer (treatment ongoing, or within 6 months or palliative) +1 Paralysis or recent plaster immobilization of the lower extremities +1 Recently bedridden for >3 d or major surgery <4 wk +1 Localized tenderness along the distribution of the deep venous system +1 Entire leg swelling +1 Calf swelling >3 cm compared to the asymptomatic leg +1 Pitting edema (greater in the symptomatic leg) +1 Previous DVT documented +1 Collateral superficial veins (nonvaricose) +1 Alternative diagnosis (as likely or > that of DVT) -2 Score >3 High probability 1 or 2 Moderate probability <0 Low probability

16. Wells Pre-Test Probability of PE Clinical Parameter Score Score Suspected DVT 3.0 Alternate Dx is less likely than PE 3.0 Heart rate >100 1.5 Immobilized or surgery in last 4 wk 1.5 Previous DVT/PE 1.5 Hemoptysis 1.0 Malignancy (treated within 6 mo.) 1.0 Score Probability Risk 0 – 2 Low 3.6% 3 – 6 Moderate 20.5% > 6 High 66.7% Wells, PS et al. Thromb Haemost. 83: 416, 2000

17. D E D Implication of D-dimer Thrombin Fibrinogen Soluble Fibrin + FP A+B FXIII Fibrin Clot Plasminogen Activators (tissue PA, urokinase PA, FXII, etc) Plasmin Plasminogen D-dimer D=D Clot + Fibrinolysis = D-dimer formation No Clot + Fibrinolysis =  D-dimer formation

18. Elevated D-dimer • DIC • Fibrinolytic therapy within 7 days • Malignancies • Aortic aneurysm, MI • Sepsis, severe infection, pneumonia • Trauma, surgery • Liver cirrhosis • Pregnancy or obstetric complication • Age • Hospitalized patients in general • Stress • Excessive exercise • Lipemic samples • Hemolyzed samples

19. Why Differences in D-dimer Assays • No D-dimer assay produces identical results to another D-dimer assay • D-dimer antigen is not homogenous but a mixture of fragments & compounds • containing fragments of D & E of different molecular weight (HMW & LMW) • D-dimer assays use different antibodies, buffers, measuring technique, standards

20. Comparability of D-Dimer Assays • Facts that effect assay comparability • No international standard for D-dimer • Different reporting units: D-dimer units (DDU) & Fibrinogen Equivalent Units (FEU) • Antibodies have different affinity to D-dimer compounds • Different reagents & assay methodologies result in different interferences • and signals • Conclusions • Each manufacturer establishes its own standardization method • Various assays have different performance characteristics • Different standardizations typically result in different quantitative results • on the same patient

21. Goals of Diagnostic Studies • Provide reliable diagnosis • Shortest possible time • Least discomfort to patient • Reasonable cost

22. PE / DVT Exclusion D-dimer Testing Algorithms

23. Low Clinical Probability of embolism Highly sensitive D-dimer assay Negative Positive Diagnosis ruled out Ventilation-perfusion scan or CT scan Algorithm for PE . Fedullo,P, Tapson, V. The Evaluation of Suspected Pulmonary Embolism. N Engl J Med 2003:1247-56.

24. Algorithm for DVT Hirsh J, Lee AY How We Diagnose & Treat Deep Vein Thrombosis, Blood 2002; 99(9): 3102-3110

25. Evaluating D-dimer Results

26. Age of Clot • Time of Initial Symptoms • Size of Clot • Where Clot Located • Anticoagulants before Draw • Patient Age • Cancer • Previous Thrombosis • Pregnant • In-patient D-dimer vs. Imaging…Why Results Do Not Agree Questions to Ask:

27. Normal D-dimer with Abnormal Scan • Distal DVT • Subsegmental / peripheral PE • Presentation to ER > 7days after symptoms • Size of clot, small clot may produce minimal D-dimer levels • Anticoagulant therapy within 24 hours

28. D-dimer vs. Imaging…Why Results Do Not Agree Age of Thrombus • Patients who report greater than 14 days duration of symptoms demonstrate inactive fibrinolysis and D-dimer levels rapidly decrease, false negative • Size of Thrombus • Smaller thrombi produce minimal levels of D-dimer, false negative Position of Thrombus • Calf vein thrombi, false negative • Sub-segmental PE, false negative Anticoagulant Therapy • Reduces fibrin formation • D-dimer levels are reduced, false negative • Do Not perform D-dimer on anticoagulated patients

29. D-dimer in Hospitalized Patients • Hospitalized patients usually have on-going disease process • D-dimer levels can be elevated in these patients due to disease state • Patients may be tested, but will likely have elevated levels in absence of clot • DO NOT perform D-dimer on hospitalized patients for DVT/PE rule-out • Utilize imaging methods for DVT/PE rule-out • D-dimer is used for DIC in hospitalized patients • Do not use hospitalized patients in a normal reference range study

30. Summary for Clinical Utility of D-dimer Assay • Negative D-dimer with low pre-test probability can exclude VTE • D-dimer is cost effective, saving thousands of dollars in health care cost • D-Dimer test results should always be used in conjunction with the patient’s medical history, pre-test probability scoring and clinical presentation.

31. Questions