What is the significance of a Prothrombin Time (PT)/International Normalized Ratio (INR) result of 18/1.7?

Significance of PT/INR 18/1.7

A PT of 18 seconds with an INR of 1.7 indicates mild coagulation abnormality that generally does not require intervention in the absence of active bleeding or planned invasive procedures. 1

Understanding PT/INR Values

PT (Prothrombin Time) and INR (International Normalized Ratio) are coagulation tests primarily designed to:

• Monitor vitamin K antagonist (warfarin) therapy 2, 1
• Assess the functionality of the extrinsic coagulation pathway 3, 4
• Evaluate liver function 3

Normal Range and Interpretation:

• Normal PT: approximately 11-13 seconds (lab-specific)
• Normal INR: 0.8-1.2
• Therapeutic INR range for most warfarin indications: 2.0-3.0 2, 1

An INR of 1.7 represents:

• If patient is on warfarin: Sub-therapeutic anticoagulation that may require dose adjustment
• If patient is not on anticoagulation: Mild coagulation abnormality that could indicate:
  • Early liver dysfunction
  • Mild vitamin K deficiency
  • Early disseminated intravascular coagulation (DIC)
  • Factor VII deficiency

Clinical Management Approach

For Patients NOT on Anticoagulation:

1. No intervention needed for INR < 2.0 without bleeding 2, 1

   • Fresh frozen plasma is not indicated for INR < 2.0 in non-bleeding patients
   • Plasma transfusion provides no clinical benefit for mild INR elevation and may cause harm 2

2. Further evaluation if clinically indicated:

   • Liver function tests if liver disease suspected
   • Additional coagulation studies if bleeding diathesis suspected
   • Vitamin K status assessment if deficiency possible

For Patients on Warfarin:

1. Dose adjustment consideration:
   • INR 1.7 is below the standard therapeutic range (2.0-3.0) for most indications 2
   • May require warfarin dose increase depending on target INR range

Special Circumstances:

1. For planned procedures:

   • Most procedures can safely proceed with INR < 2.0 1
   • Some high-risk procedures may require normalization of INR

2. For active bleeding:

   • More urgent intervention may be needed based on bleeding severity
   • Consider vitamin K administration and/or factor replacement if clinically indicated

Common Pitfalls to Avoid

1. Treating the laboratory value rather than the patient

   • Avoid unnecessary plasma transfusion for mild INR elevation (1.0-2.0) in non-bleeding patients 2, 1
   • Clinical context should guide intervention decisions

2. Pre-analytical errors affecting results

   • Underfilled collection tubes
   • Improper citrate concentration
   • Prolonged storage before testing 1

3. Misinterpretation in liver disease

   • INR was designed for warfarin monitoring, not liver disease assessment 2
   • May not accurately predict bleeding risk in liver disease 1

4. Failure to recognize lupus anticoagulant

   • Can cause variability in INR measurements 1
   • Consider specialized testing if suspected

Remember that INR was specifically designed for monitoring vitamin K antagonist therapy and has limited validity as a general coagulopathy screen in patients not on anticoagulation 2, 1.