What do you order PT (Prothrombin Time)/INR (International Normalized Ratio) and PTT (Partial Thromboplastin Time) for in the Emergency Department (ED)?

PT/INR and PTT Testing Indications in the Emergency Department

PT/INR and PTT should be ordered in the ED primarily for patients with suspected bleeding disorders, those on anticoagulant therapy, or patients with active bleeding requiring evaluation of coagulation status. 1

Primary Indications for PT/INR and PTT Testing

1. Anticoagulant Therapy Evaluation

• For patients on Vitamin K Antagonists (VKAs) like warfarin:

  • PT/INR is the standard test for monitoring therapeutic levels 2
  • Target INR typically 2.0-3.0 for most indications, 2.5-3.5 for mechanical heart valves 2
  • Normal PT/INR excludes clinically significant warfarin effect

• For patients on heparin therapy:

  • PTT is the primary test for monitoring unfractionated heparin (UFH) 1
  • Anti-Xa levels may be more appropriate for low molecular weight heparin (LMWH) 1

• For patients on Direct Oral Anticoagulants (DOACs):

  • PT and/or PTT can provide qualitative assessment of anticoagulant activity 1
  • Normal thrombin time (TT) excludes clinically relevant dabigatran levels 1
  • Specialized tests like dilute thrombin time, ecarin clotting time, or anti-Xa assays are preferred but often not readily available in ED settings 1

2. Active Bleeding Evaluation

• For patients with clinically relevant bleeding:
  • PT/INR and PTT should be requested in all such patients 1
  • Helps determine if coagulopathy is contributing to bleeding
  • Guides reversal strategies for anticoagulated patients

3. Pre-Procedural Assessment

• For patients requiring urgent procedures:
  • PT/INR and PTT help determine bleeding risk 1
  • Particularly important for high bleeding risk procedures (neurosurgery, spinal procedures) 1
  • Results guide the need for reversal agents or blood product administration

4. Suspected Coagulopathy

• For patients with suspected bleeding disorders:
  • Helps screen for factor deficiencies in the extrinsic (PT) or intrinsic (PTT) coagulation pathways
  • May indicate need for further specialized testing

Clinical Scenarios Requiring PT/INR and PTT Testing

1. Trauma patients with suspected bleeding

   • Particularly elderly patients on anticoagulants 1
   • Helps guide transfusion and reversal strategies

2. Patients with intracranial hemorrhage

   • Critical to determine if anticoagulation is contributing 1, 3
   • Guides urgent reversal decisions

3. Stroke patients being considered for thrombolytic therapy

   • Normal PT/PTT required for rt-PA administration 3
   • Can be predicted with 100% sensitivity in patients taking warfarin/heparin or on hemodialysis 3

4. Patients with GI bleeding

   • Helps determine if coagulopathy is contributing
   • Guides correction strategies if needed

Important Caveats and Pitfalls

1. INR limitations:

   • INR was specifically designed for monitoring VKA therapy and has limited validity in other settings 1
   • Using INR as a universal coagulation marker is inappropriate 1, 4
   • Mildly elevated INR (<2.0) in non-anticoagulated patients rarely requires correction 1

2. Test interpretation challenges:

   • Normal PT/PTT doesn't exclude all bleeding disorders
   • PT/INR doesn't reflect factor IX levels, which can contribute to bleeding risk even with therapeutic INR 5
   • Results can vary between laboratories due to reagent and instrument differences 6

3. DOAC monitoring limitations:

   • Standard PT/PTT has limited sensitivity for DOACs 1
   • Specialized tests are preferred but often not available in emergency settings 1

4. Unnecessary testing:

   • Avoid routine PT/INR/PTT screening in patients without bleeding symptoms, anticoagulant use, or need for urgent procedures
   • Targeted testing based on clinical presentation is more appropriate

Algorithm for PT/INR and PTT Testing in ED

1. Is the patient on anticoagulant therapy?

   • If yes → Order appropriate test (PT/INR for warfarin, PTT for heparin)
   • If DOAC → Consider PT/PTT as screening test, recognize limitations

2. Does the patient have active bleeding?

   • If yes → Order both PT/INR and PTT

3. Does the patient need an urgent procedure with bleeding risk?

   • If yes → Order both PT/INR and PTT

4. Is there suspicion for an inherited or acquired coagulopathy?

   • If yes → Order both PT/INR and PTT as initial screening

5. Is the patient being evaluated for thrombolytic therapy?

   • If yes → Order both PT/INR and PTT unless patient has no risk factors for abnormal results 3

Remember that PT/INR and PTT are screening tests and may need to be supplemented with more specialized coagulation assays depending on the clinical scenario.