Evaluation of Complex Coagulation Cases: Case-Based Illustrations of Important Issues

Transcription

1 Evaluation of Complex Coagulation Cases: Case-Based Illustrations of Important Issues Kristi J. Smock, MD Associate Professor of Pathology University of Utah Health Sciences Center Medical Director, Hemostasis/Thrombosis Laboratory ARUP Laboratories

2 Objectives Review several coagulation cases that demonstrate interpretive challenges Discuss how clinical information and knowledge of coagulation test methodologies are essential for proper interpretation of coagulation testing Highlight the role of coagulation laboratory professionals in resolving challenging cases

3 Case 1 49-year-old male who was exposed to heparin during treatment for an MI and was suspected to have HIT. During his hospital care, marked elevations of his PT and aptt and low fibrinogen were noted. He received multiple units of FFP and cryoprecipitate without improvements in his clotting times or fibrinogen. A battery of follow-up testing was sent to our laboratory.

4 Some of our results Test Result Reference Interval PT 47.3 sec sec aptt 120 sec sec aptt 1:1 imm 105 sec sec Thrombin Time >127 sec sec Reptilase Time 17.6 sec <22 sec What additional history could be useful? What can you conclude so far? What do you suspect?

5 Thrombin time and reptilase time Thrombin Anticoagulants (heparin, DTIs) Fibrinogen Fibrin Reptilase Prolonged TT and RT Low fibrinogen Abnormal fibrinogen Increased FDPs Paraproteins Prolonged TT with normal RT Unfractionated heparin Direct thrombin inhibitors (DTIs)

6 Case 1, continued Additional history indicated that the patient was being treated for HIT with argatroban while HIT testing was pending Would argatroban be expected to cause all the abnormalities observed?

7 Intrinsic Pathway Damaged Surface, HMWK, Kallikrein XII XIIa Argatroban = parenteral DTI Prolongs PT and aptt Affects fibrinogen assay? Thrombin XI VIII IX Thrombin Common Pathway XIa VIIIa V X IXa Thrombin Va Phos, Ca 2+ Xa Phos, Ca 2+ Extrinsic Pathway Tissue Injury Tissue Factor Phos, Ca 2+ VIIa VII II IIa (Thrombin) Fibrinogen Fibrin XIIIa Cross-linked Fibrin

8 Fibrinogen assay Thrombin Anticoagulants (high heparin or DTI levels) Fibrinogen Fibrin Common fibrinogen assay is a modified thrombin time (Clauss fibrinogen) Calibrated method that derives fibrinogen activity from the rate of clot formation Evaluates fibrinogen amount and function (activity assay) Therapeutic heparin and direct thrombin inhibitors often don t interfere Thrombin reagent is present in excess Commercial reagents often contain a heparin neutralizer High heparin or direct thrombin inhibitor levels can cause falsely low fibrinogen in this method

9 Case 1, conclusion The observed coagulation abnormalities were attributed to argatroban effect HIT was ruled out after HIT lab testing The patient s coagulation testing returned to normal once all anticoagulation was discontinued

10 Case 2 63-year-old male with sagittal sinus thrombosis. Thrombophilia work-up was sent to our laboratory. We observed unusual patterns in the testing and discussed the case with the ordering physician.

11 Lupus anticoagulant testing Test Result Reference Interval PT 13.3 sec sec aptt 55 sec sec Thrombin Time 118 sec sec aptt hep neut 54 sec sec aptt 1:1 imm 50 sec sec DRVVT 90 sec sec DRVVT 1:1 59 sec sec Lupus anticoagulant confirmatory testing Positive in both the aptt and DRVVT Negative

12 Other thrombophilia testing Test Result Reference Interval Antithrombin activity Antithrombin antigen 109% % 97% % Protein C activity 172% % Protein C total antigen 104% % Protein S activity 167% % Protein S free antigen 99% %

13 Case 2, continued Discussion with the ordering physician revealed that the patient was treated for his thrombotic event with the dabigatran. Dabigatran is a direct oral anticoagulant (DOAC) that is a direct thrombin inhibitor. How does dabigatran affect routine and specialized coagulation testing?

14 Dabigatran and routine coagulation assays PT/INR is insensitive to dabigatran and may be normal at typical on-therapy or even above ontherapy drug levels aptt is more sensitive to dabigatran than PT/INR but has a curvilinear response curve Normal aptt suggests little anticoagulant effect aptt may not be prolonged at on-therapy trough levels in some patients Differences in sensitivity between aptt reagents Thrombin time is very sensitive to dabigatran Cuker et al. Hematology Am Soc Hematol Educ Program (2015)

15 Dabigatran test summary First published in Hospital Practice 2011;39:23-34 Hospital Practice, a division of JTE Multimedia, LLC

16 DOACs interfere with many specialized coagulation tests DOACs directly inhibit factors in the common pathway of the coagulation cascade, either thrombin (IIa) or Xa Many coagulation tests are functional measurements of coagulation factors/reactions (clot-based, chromogenic substrate) and can be affected by DOACs Antigen measurements are not affected but are usually not the recommended first-line tests Best to avoid specialized coagulation testing in patients on DOACs Many assays are optimized to diminish the effects of traditional anticoagulants (warfarin, heparin) but this is not currently possible for DOACs (no neutralizing agents for lab use) Have a low threshold for suspecting test interference if results are unexpected in a patient on a DOAC

17 DOACs interfere with many specialized coagulation tests Fibrinogen assays Potential under-estimation of activity Factor assays Potential under-estimation of activity Lupus anticoagulant testing Potential false-positive or false-negative results Thrombophilia testing Potential false-negative for APC resistance Potential over-estimation of activity for proteins C, S, antithrombin Note: Effects are method dependent Adcock DM and Gosselin R. Thromb Res 2015;136:7-12

18 aptt (sec) Protein C activity assay 160 Protein C Activity Calibration Activity (%) aptt (sec) % 25% 12.5% 50% 100% Activity (%)

19 Case 2, conclusion Dabigatran interference is observed in the patient s lupus anticoagulant and protein C and S activity testing, interference with antithrombin activity is not clearly present The lupus anticoagulant results may represent a false-positive; a lupus anticoagulant cannot be confirmed or excluded Functional deficiencies of protein C and S can t be entirely excluded

20 Case 2, conclusion, continued Consultation with laboratory professionals helps to avoid acting on potentially erroneous results What laboratory professionals can do Implement protocols for identification of interfering substances Alert providers when unusual and potentially unreliable test results are observed Utilize interpretive comments that provide information about common interfering substances Provide additional education about interfering substances in the form of websites, publications, etc.

21 Case 3 79-year-old female with Waldenstrom macroglobulinemia with prolonged clotting times and no bleeding, liver dysfunction, or DIC underwent an extensive workup to determine the cause of her clotting time abnormalities

22 Some of our results Results Serum Viscosity ( ) PT ( sec) PT 1:1 Mix aptt (32-48 sec) aptt 1:1 Mix Set # Set # N/A At time point #1 a battery of factor assays (II, V, VII, VIII, IX, X, XI, and XII) demonstrated low factor activities and nonparallelism Do multiple factor deficiencies make clinical sense? What could be the cause of the coagulation test abnormalities?

23 Case 3, conclusion Paraprotein interference is observed in the patient s clotting times and other clot-based testing Paraproteins can impede fibrin polymerization, resulting in prolonged clotting times Can result in inhibitor pattern in mixing studies, falsely low fibrinogen or other factor activities, false-positive Bethesda assays, and other coagulation test abnormalities High paraprotein levels can also cause a bleeding diathesis Kotlin et al. Acta Haematol 2008;120:75-81

24 Thank you for your attention, any questions?