Consultative Coagulation How to Effectively Answer Common Questions About Hemostasis Testing Session #5000 Dorothy M. (Adcock) Funk, M.D. Karen A. Moser, M.D. Esoterix Coagulation September 20, 2013
Disclosures Dr. (Adcock) Funk and Dr. Moser: In the past 12 months, I have not had a significant financial interest or other relationship with the manufacturer(s) of the product(s) or provider(s) of the service(s) that will be discussed in my presentation.
Topic Overview D-dimer assays Use and pitfalls Direct Oral Anticoagulants Effects on coagulation assays Thrombophilia Evaluation Who, when, and what to order?
D-dimer- Use and Pitfalls
Use of D-Dimer Assay for Exclusion of VTE D-dimer is a terminal degradation product of cross-linked fibrin Patients with acute venous thrombosis (VTE) have increased levels of D-Dimer A negative D-Dimer therefore, can be used to rule out VTE D-dimer has its greatest utility for its negative predictive value But an appropriate assay must be used and the assay must be used appropriately
Use of D-Dimer Assay for Exclusion of VTE D-dimer is a powerful adjunct when used with other diagnostic or clinical assessment modalities No single test, including the D-dimer assay, has sufficient sensitivity and specificity to be used alone in the diagnosis or exclusion of venous thrombosis Standardized clinical assessments using risk factors and presenting findings can be used to reproducibly and accurately determine the likelihood that a patient has DVT or PE Patients are scored as VTE likely or VTE unlikely or low, intermediate or high probability of VTE or non-high probability of VTE
Use of D-Dimer Assay for Exclusion of VTE Patients classified as VTE likely or high probability of VTE : D-dimer testing is not warranted Appropriate diagnostic imaging tests should be performed Patients classified as unlikely or lowintermediate or non-high clinical probability of VTE: a D-dimer value below the exclusion threshold value (negative D-dimer) excludes VTE and no further diagnostic procedures to exclude VTE need be performed As long as the assay is cleared for exclusion of DVT and/or PE
Use of D-Dimer Assay for Exclusion of VTE A variety of commercial D-dimer kits are available, not all are appropriate to be used in the exclusion of VTE How is the assay labeled by the FDA: F FDA cleared for exclusion of venous thrombosis For DVT, PE or both F Aid in Diagnosis For DVT, PE or both
Use of D-Dimer Assay for Exclusion of VTE FDA cleared for exclusion of VTE Negative D-dimer: in patients with a non-high clinical probability of VTE effectively excludes VTE No further testing required FDA cleared as an aid in diagnosis Negative D-dimer: regardless of clinical probability, one or more additional tests, (usually objective imaging studies) are required to rule out VTE D-dimer results should not be used in an exclusion strategy
Supporting Evidence Used to Discriminate Indications for Use* Discrimination Criteria Indications for Use Product Claims Aid in the Diagnosis of VTE Exclusion of VTE External studies Method comparison study Patient management study Number of samples Validation criteria Statistically significant number of outpatient samples with known VTE diagnosis (> 10% prevalence for both DVT and PE) D-dimer values are compared to a predicate D-dimer device Sensitivity Not defined > 95% NPV > 97% > 97% Statistically significant number of consecutively eligible outpatients presented to an emergency department or outpatient clinic with suspicion of VTE (> 10% prevalence for both DVT and PE) D-dimer values are compared to final outcome (clinical truth) through imaging techniques and, if the imaging studies fail to confirm VTE, a threemonth patient follow-up is needed to confirm a negative result. * CLSI H59
Use of D-Dimer Assay for Exclusion of VTE D-dimer for VTE Exclusion: Cannot be used to exclude upper extremity DVT Cannot be used to exclude arterial thrombosis Cannot be used when patients have been on anticoagulant therapy for >24 hours Not recommended if the DVT is distal to the knee Not recommended in a pediatric population Not recommended in situations where levels are commonly elevated: Hospitalized population Pregnant population
Use of D-Dimer Assay for Exclusion of VTE Recommendations CAP Proficiency Data Use only a quantitative assay FDA cleared for evaluation of VTE Use the threshold for VTE evaluation given by the manufacturer Use type and magnitude of unit given in the package insert Clearly distinguish reference interval and threshold value for VTE exclusion on report Follow package insert instructions Olson JD et al. Arch Pathol Lab Med. 2013; 137:1030-1038.
Factors Affecting D-Dimer Levels Clot Composition: white or platelet rich (arterial) vs red or fibrin rich (venous) clot Clot Size: Arterial clots - pea sized, platelets predominate Venous clots - considerably larger, fibrin and red blood cells predominate Proximal and larger venous blood clots are associated with higher D-dimer levels than thrombi distal to the knee. Clot Age: highest levels of D-dimer are seen early in the disease process
VTE with Negative D-Dimer Rare situation (< 2% of cases) usually due to one of the following: Small thrombosis (often distal or pediatric patient) Initiation of anticoagulant therapy > 24 hours before measuring D-dimer Period too long between the onset of clinical symptoms and blood sample collection False positive result from radiology Fibrinolysis deficiency (tpa deficiency or high PAI level)
Case # 1 A 55 y/o man with psoriatic arthritis presents with pain/swelling in the left calf 3 days following immobilization due to a broken foot. Which of the following is correct? A. A positive D-dimer would confirm the dx of DVT. B. A negative D-dimer that is FDA approved as an aid in the diagnosis would rule out DVT. C. A D-dimer is not indicated as this patient is high probability for DVT.
Case # 2 A 22 y/o woman on OCP for 4 months presents to her PCP with a complaint of pain/swelling of the right calf for about the past 8 weeks. A D-dimer is performed but falls below the established cut-off for exclusion of VTE. Her physician orders an ultrasound which is positive for VTE and calls the pathologist to report your D-dimer test is not any good. How would you respond?
Direct Oral Anticoagulant Agents Brief Overview of Effects on Coagulation Assays
New Oral Anticoagulant Agents Direct Thrombin Inhibitors Dabigatran Direct Xa Inhibitors Rivaroxaban Apixaban Edoxaban
Coagulation Cascade: Effect of Direct Thrombin Inhibitors FXII FXI FIX APTT FVIII FVII PT FV FII FX Thrombin Direct Thrombin Inhibitor Fibrinogen ØTCT Fibrin
Dabigatran Effect on APTT* * Lindahl TL. Thromb Haemost 2011;105:371-378
Dabigatran Effect on PT* * Lindahl TL. Thromb Haemost 2011;105:371-378
Coagulation Cascade: Effect of Direct Xa Inhibitor FXII FXI FIX APTT FVII PT FVIII FII FV FX Thrombin Xa Inhibitor Fibrinogen TCT Fibrin
Dabigatran and Rivaroxaban Effect on Coagulation Assays Drugs act as inhibitors in the laboratory: Incomplete correction with 1:1 plasma mix Non specific inhibitor effect in factor assays Can cause a false positive Bethesda assay False positive Lupus Anticoagulant Assays False normal APCR Dabigatran: falsely low FXIII activity No effect on: D-dimer, VWF assays, free protein S antigen, chromogenic protein C activity, reptilase time
Effect of Dabigatran on Factor Assays Factor Activity in IU/dL 1.5 1 0.5 0 0 25 50 75 100 125 150 200 300 400 500 FVIII 0.99 0.66 0.51 0.48 0.38 0.32 0.25 0.16 0.09 0.07 0.06 FIX 1.40 0.80 0.66 0.60 0.50 0.42 0.37 0.28 0.16 0.09 0.08 FXI 0.93 0.80 0.66 0.64 0.58 0.51 0.46 0.41 0.30 0.24 0.20 Intrinsic Factors APTT-Based Extrinsic Factors PT-Based * Adcock DM, et al. AJCP. 2013;139:102-1104.
Dabigatran and Rivaroxaban Effect on Coagulation Assays % change compared to Reference Plasma 200 175 150 125 100 75 50 25 0 Dabigatran Rivaroxaban AT assays either Laboratory IIa Xa based Assays PC and PS assays: clot-based
Case # 3 33 y/o woman suffers a post-partum DVT and is treated with rivaroxaban. Her physician orders a thrombophilia work-up; patient has the lab work drawn 2 days after starting tx. The following assays were performed: Protein S (PS) activity (clot based): normal Protein C (PC) activity (chromogenic): decreased APCR ratio: normal drvvt confirm is positive with negative Staclot LA and negative acl and B2GP1 IgG and IgM
Case # 3, continued The physician calls you for help with the interpretation and you respond: A. PS activity and APCR can both be falsely normal and LA can be falsely abnormal (positive) B. The low PC may be due to the anticoagulant C. All coagulation testing is unreliable due to the rivaroxaban
Thrombophilia Evaluation Who, When, and What to Order?
Thromboembolic Disease Venous or Arterial Venous Thrombosis Low flow system Fibrin rich Common risk factors: stasis, vascular injury and changes in blood composition Current literature suggests that venous and arterial thrombosis share common risk factors Arterial thrombosis High flow/pressure Platelet rich Typically occurs in setting of vessel wall damage (atheroma) ASVD risk factors Increased lipids Hypertension Diabetes mellitus
Venous Thromboembolic Disease Current Concepts A complex, multi-factorial disorder in which physiologic, acquired (environmental) and genetic risk factors interact to determine risk of thrombus development Clear evidence VTE is a culmination of a complex interaction of different mutations involving distinct genes +/- environmental factors Estimated that 60% or more of VTE predisposition due to genetic components* *GAIT Study: Souto JC et al. Am J Hum Genet. 2000;67:1452
Thrombotic Threshold Trait Rosendaal FR. Lancet. 1999; 353:1167
Hemostasis is highly complex, involving multiple, extensively regulated pathways. Hereditary thrombophilic risk factors may fall within multiple different pathways. Anticoagulant Factors flat, PC, PS, PZ TFPI, HC II Profibrinolytic Factors fltpa Clot formation Factor V Leiden FII G20210A FVIII,IX,XI,Fib Clotting Factors Clot lysis PAI-1 Lipoprotein (a) Antifibrinolytic Factors
Thrombophilia and Pregnancy Increased risk VTE during pregnancy and puerperium The following associations are controversial Fetal loss Recurrent first trimester abortion Stillbirth (second and third trimester loss) Abruptio placentae Severe pre-eclampsia (HELLP Syndrome) Intrauterine growth retardation
Laboratory Evaluation for Thrombophilia When is testing indicated? Venous thrombosis Hx of recurrent VTE VTE prior to 50 years of age Unprovoked VTE in patients of any age Patients with VTE and family hx of VTE VTE in association with pregnancy, OCP, or HRT VanCott E et al. Arch Pathol Lab Med. 2002; 126:1281-195. Baglin T et al. Br J Haematol. 2010;149(2):209-220
Laboratory Evaluation For Thrombophilia When is testing NOT indicated: In unselected patients with upper extremity VTE Central venous catheter associated thrombosis Case finding of asymptomatic relatives with FV Leiden or FII G20210A Retinal vein occlusion Arterial thrombosis Identification of risk for hospital-associated VTE Questionable Significance First episode intra-abdominal thrombosis First episode cerebral vein thrombosis Baglin T et al. Br J Haematol. 2010;149(2):209-220
Laboratory Evaluation Thrombophilia Basic Panel AT Activity PC Activity Free PS Ag Activated Protein C Resistance or Factor V Leiden Factor II G20210A Lupus anticoagulant screen with at least 2 different assay types ACA and B 2 GP1 IgG, IgM Homocysteine (controversial) Factor VIII Activity (controversial) Seligsohn U, Lubetsky A. N Engl J Med. 2001; 344(16):1222-31. VanCott E et al. Arch Pathol Lab Med. 2002; 126:1281-195. Baglin T et al. Br J Haematol. 2010;149(2):209-220
AT, PC or PS Deficiency Recommended screening assays Antithrombin Activity - Chromogenic Protein C Activity Chromogenic Free Protein S Antigen ELISA None are clot-based activity assays Any condition that increases or decreases clotting time can affect activity
Laboratory Evaluation Thrombophilia Additional Testing Fibrinogen Activity and Antigen (Dysfibrinogenemia) Factor IX, XI Activity Lipoprotein (a) PAI-1 Activity JAK-2 (Janus-activating kinase-2) Flow for PNH Unexplained intra-abdominal thrombosis PAI-1 4G/5G Mutation MTHFR C677T, MTHFR A128C FV HR2 Haplotype Generally of no value
Laboratory Evaluation For Thrombophilia Must confirm abnormal plasma based assays before establishing diagnosis Due to high false positive rate Many drugs and physiologic conditions influence results Should consider evaluation of family
Laboratory Evaluation Timing is critical to result interpretation Values for AT, PC and PS may be decreased in: Acute phase of thrombosis Severe liver disease Post operative state Severe illness Disseminated intravascular coagulation (DIC) Nephrotic syndrome (PS may increase) L-asparaginase therapy (largely affects AT) Newborn period always consider the patient s age!
Laboratory Evaluation Timing is critical to result interpretation Heparin therapy Decreases AT levels Vitamin K antagonist (warfarin) therapy Decrease PC/PS/PZ activity PC or PS Ag/FVII or FIX Ag not recommended Direct Oral Anticoagulants Falsely elevated AT/PC/PS and APCR False positive LA testing Evaluation during pregnancy PS levels may decrease significantly Increased FVIII and fibrinogen
Pitfalls in Thrombophilia Testing PS and clot-based PC activity can be falsely reduced in patients with FVL PS and clot-based PC activity can be falsely elevated with an elevated baseline clotting time Incidence of hereditary AT,PC, PS deficiency is lower than the incidence of a falsely low result More likely to have a false positive than a true positive result
Case # 4 23 y/o woman develops DVT in her 2 nd trimester. A thrombophilia evaluation reveals low protein S activity at 45%. What do you tell her physician?
Case # 5 A 37 y/o man with a heterozygous factor V Leiden mutation also has a low protein S activity at 52%. How do you interpret these results?
Case # 6 A 54 y/o man immediately following an acute thrombosis has an AT activity of 54%. Repeat AT activity 3 months later is normal. How do you explain this to his physician?
Thank you for your participation! Questions? adcockd@labcorp.com moserk@labcorp.com