Diagnostic Algorithms in VTE

Transcription

1 Diagnostic Algorithms in VTE Mark H. Meissner, MD Department of Surgery University of Washington School of Medicine

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3 Overutilization of Venous Duplex U/S (Zweibel et al, Australasian Rad, 1995) 1000% increase in non-invasive exams 50% decrease in contrast venography Incidence of (+) studies Validation studies - 25% Clinical use - < 10% Implications of overutilization Economic costs Strained resources Limited diagnostic utility

4 Diagnostic Test Diagnostic Predictive Value Sensitivity 97%, specificity 94% for proximal DVT However. Positive & negative predictive value more relevant Disease State DVT (+) DVT (-) Ultrasound (+) True Positive TP False Positive FP Ultrasound (-) False Negative FN True Negative TN PPV = TP / TP + FP NPV = TN / TN + FN

5 Predictive Value Bayes Theorem and Venous U/S P(DVT + Duplex) = P(DVT + Duplex) X P(DVT)/P(+ Duplex) Predictive value depends on pretest probability of disease NPV PPV 10% Prevalence 25% Prevalence 70% PPV 90% PPV Disease Prevalence Optimizing utilization optimizes patient care

6 Alternative Approaches to Diagnosis Clinical Risk Stratification D-Dimer testing Combined strategies

7 Clinical Risk Stratification Wells et al, Lancet 1997 Active Cancer Criteria Paralysis, paresis or recent plaster immobilization Surgery < 4 weeks, Bedridden > 3 days Thigh + calf swelling on the affected side Tenderness along the deep venous system Affected calf > 3cm larger than the other side Pitting edema (greater in the affected leg) Collateral superficial veins Score 1 point 1 point 1 point 1 point 1 point 1 point 1 point 1 point Alternative diagnosis as likely or greater than DVT - 2 points Probability: Low 0 points; Moderate 1-2 points; High 3 points

8 Pretest Probability Wells et al, Lancet 1997 & Thromb Haemost 1999 Outpatient Inpatient Probability Points N (%) DVT (%) N (%) DVT (%) Low % 3% 33% 10% Moderate % 17% 47.3% 19.7% High 3 12% 75% 19% 76%

9 D-Dimer in Venous Thromboembolism Sensitive for in vivo crosslinked fibrin generation 98% sensitive for venous thromboembolism 30-40% specificity Venous thromboembolism Malignancy Infection Trauma Surgery Pre-eclampsia Highest negative predictive value in outpatients Low prevalence of DVT Low incidence of concurrent illness

10 D-Dimer Management Trials (Perrier et al, Lancet 1999) Suspected DVT / PE Prospective management trial 918 consecutive patients Clinical Assessment + D-Dimer < 500 ng/ml Tx Withheld > 500 ng/ml 286 managed with negative D-Dimer alone U/S 2.6% 3 month thromboembolic risk (suspected DVT)

11 Limitations of D-Dimer Levels depend on Prior anticoagulant use Age of thrombus Isolated calf vein thrombosis NPV dependent on pretest probability Low probability - 100% Moderate probability % High probability %

12 Combined Diagnostic Strategies Focuses on low probability patients (Wells criteria) Constitute approximately 50% of U/S referrals 2% - 3% incidence of DVT Low incidence of comorbid conditions NPV of D-Dimer in low probability patients Author N Low Prob (%) Dimer (-) Dimer (-) NPV DVT (+) DVT (-) Bucek (56%) % Anderson (55%) % Dryjski 66 7 (10%) % Total (49%) %

13 D-Dimer in Non-High Probability Patients Schutgens REG et al; Circulation consecutive outpatients 533 (65.7%) low or moderate probability Suspected DVT Normal D-Dimer Abnormal D-Dimer Non-High PTP No Further Testing 0.6% VTE at 3 months High PTP Ultrasonography Serial Ultrasonography

14 Combined Diagnostic Strategies Validated combined diagnostic strategies Outpatients No PE symptoms No anticoagulants No prior DVT Diagnostic approach Low PTP - (-) D-Dimer requires no further testing Moderate PTP - Depends on D-Dimer assay High PTP -Requires U/S Local validation required (particularly moderate PTP) Inpatient strategies less well developed

15 Clinical Decision Rules for PE Wells Score Clinical Feature Points Clinical Feature Points Previous PE or DVT 1.5 Age > 65 yrs 1 Heart rate > Previous PE or DVT 3 Recent surgery/immobilization 1.5 Surgery/fracture within 1 mo 2 Signs of DVT 3 Active malignancy 2 Alternative Dx > PE 3 Unilateral limb pain 3 Hemoptysis 1 Hemoptysis 2 Cancer 1 Heart rate Probability: Low < 2; Intermediate 2 6; High > 6 Revised Geneva Score Pain on palpation + edema 4 Probability: Low 3; Intermediate 4-10; High > 11

16 Diagnostic Algorithms for PE Suspected PE Clinical Decision Rule Low Probability Intermediate Probability High Probability Negative D-Dimer Positive Multi-Row- Detector CTPA No Treatment Negative No Treatment Positive Treat

17 Conclusion Over-utilization of diagnostic studies is bad health care Diagnostic strategies depend on a high NPV in low probability patients Limitations of isolated diagnostic studies U/S & CTPA Misuse of resources Limited PPV with low disease prevalence Risk stratification 3% DVT in low probability patients 4 15% PE in low probability patients D-Dimer Low specificity requires many (-) U/S studies Unacceptable NPV in high probability patients Combined strategies maximize utility of individual studies