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Coagulation Test Interpretation in a Patient Taking Direct Oral Anticoagulant Therapy

Educational Objective
Based on this clinical scenario and the accompanying image, understand how to arrive at a correct diagnosis.
1 Credit CME

A 74-year-old man presented with spontaneous, acute onset of confusion and headache. He had no preceding head trauma or falls. He had a history of atrial fibrillation with an annual stroke risk of 2.9% (based on points accrued for hypertension and age ≥65 years using the CHA2DS2-VASc score1). He was being treated with rivaroxaban, 20 mg daily. He took his last dose 14 hours prior to presentation. Other medications included ramipril and rosuvastatin.

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B. The patient’s hemostatic status is not appropriate for surgery because the abnormal PT suggests anticoagulant effect from rivaroxaban.

Prothrombin time (PT) and activated partial thromboplastin time (aPTT) are clot-based tests that measure the length of time required for thrombus formation in the presence of specific reagents. PT measures the activity of extrinsic (factor VII) and common (factors II, V, X) coagulation pathways and was originally introduced for monitoring vitamin K antagonist therapy (eg, warfarin).2 aPTT measures the activity of intrinsic (factors VIII, IX, XI, and XII) and common coagulation pathways and was developed as a preoperative screen for hemophilia in high-risk individuals, but later validated for monitoring therapy with unfractionated heparin.3

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Article Information

Corresponding Author: Michelle Sholzberg, MD, MSc, Coagulation Laboratory, St. Michael's Hospital, 30 Bond St, Toronto, ON M5B 1W8, Canada (sholzbergm@smh.ca).

Published Online: September 14, 2018. doi:10.1001/jama.2018.13998

Conflict of Interest Disclosures: The authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest and none were reported.

Additional Contributions: We thank the patient for granting permission to publish this information.

References
1.
Lip  GY, Lane  DA.  Stroke prevention in atrial fibrillation: a systematic review.  JAMA. 2015;313(19):1950-1962. doi:10.1001/jama.2015.4369PubMedGoogle ScholarCrossref
2.
Hylek  EM, Go  AS, Chang  Y,  et al.  Effect of intensity of oral anticoagulation on stroke severity and mortality in atrial fibrillation.  N Engl J Med. 2003;349(11):1019-1026.PubMedGoogle ScholarCrossref
3.
Kitchens  CS.  To bleed or not to bleed? is that the question for the PTT?  J Thromb Haemost. 2005;3(12):2607-2611. doi:10.1111/j.1538-7836.2005.01552.xPubMedGoogle ScholarCrossref
4.
Cuker  A, Siegal  DM, Crowther  MA, Garcia  DA.  Laboratory measurement of the anticoagulant activity of the non-vitamin K oral anticoagulants.  J Am Coll Cardiol. 2014;64(11):1128-1139. PubMedGoogle ScholarCrossref
5.
Jabet  A, Stepanian  A, Golmard  JL,  et al.  Are screening tests reliable to rule out direct oral anticoagulant plasma levels at various thresholds (30, 50, or 100 ng/mL) in emergency situations?  Chest. 2018;153(1):288-290. PubMedGoogle ScholarCrossref
6.
Tomaselli  GF, Mahaffey  KW, Cuker  A,  et al.  2017 ACC Expert Consensus Decision Pathway on Management of Bleeding in Patients on Oral Anticoagulants.  J Am Coll Cardiol. 2017;70(24):3042-3067. PubMedGoogle ScholarCrossref
7.
Heidbuchel  H, Verhamme  P, Alings  M,  et al.  European Heart Rhythm Association Practical Guide on the use of new oral anticoagulants in patients with non-valvular atrial fibrillation.  Europace. 2013;15(5):625-651. PubMedGoogle ScholarCrossref
8.
Gosselin  RC, Adcock  DM, Bates  SM,  et al.  International Council for Standardization in Haematology (ICSH) recommendations for laboratory measurement of direct oral anticoagulants.  Thromb Haemost. 2018;118(3):437-450.PubMedGoogle Scholar
9.
Bates  SM, Weitz  JI.  Coagulation assays.  Circulation. 2005;112(4):e53-e60. PubMedGoogle ScholarCrossref
10.
Antovic  JP, Skeppholm  M, Eintrei  J,  et al.  Evaluation of coagulation assays versus LC-MS/MS for determinations of dabigatran concentrations in plasma.  Eur J Clin Pharmacol. 2013;69(11):1875-1881. PubMedGoogle ScholarCrossref
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