Does Deflazacort (corticosteroid) affect Prothrombin Time (PT) and International Normalized Ratio (INR)?

Deflazacort's Effect on PT/INR

Deflazacort does not directly affect Prothrombin Time (PT) or International Normalized Ratio (INR) values, as corticosteroids are not known to interfere with the coagulation pathways measured by these tests.

Understanding PT/INR Testing

• PT/INR testing specifically evaluates the extrinsic and common coagulation pathways, including factors II, V, VII, X, and fibrinogen 1
• The INR was specifically designed and validated to assess coagulation status only in patients receiving vitamin K antagonist therapy, not as a general predictor of bleeding risk 2
• INR is calculated using the patient's PT, mean normal PT, and the international sensitivity index (ISI) of the thromboplastin reagent according to the formula: INR = [PTpatient/PTnormal]^ISI 3

Factors That Affect PT/INR

• PT/INR values are primarily affected by:

  • Vitamin K antagonist therapy (warfarin) 3
  • Liver dysfunction affecting synthesis of clotting factors 3, 4
  • Consumption of coagulation factors (e.g., DIC) 1
  • Lupus anticoagulant (in some cases) 3

• Corticosteroids like deflazacort are not documented to directly interfere with the coagulation cascade measured by PT/INR 2, 1

Clinical Implications

• When monitoring patients on vitamin K antagonists (VKA):

  • The therapeutic INR range is typically 2.0-3.0 (target 2.5) 3
  • Variability in thromboplastin reagents can lead to differences in INR results between laboratories 5, 6
  • Medications that don't directly affect coagulation factors (like deflazacort) would not be expected to alter PT/INR values 2

• For patients with liver disease:

  • Standard INR (designed for VKA monitoring) may not be appropriate and could require a modified INR calculation 3, 7
  • Activity percentage expression may provide better standardization than INR in liver failure 4

Important Considerations

• While deflazacort itself doesn't directly affect PT/INR, be aware that:

  • Long-term corticosteroid use may indirectly affect coagulation through other mechanisms (e.g., potential effects on liver function in some patients)
  • INR measurements typically don't vary significantly throughout the day in stable patients 8
  • The INR scale is only validated for patients on VKA with no other superimposed coagulation defects 3

• For accurate PT/INR interpretation:

  • Consider the clinical context (whether patient is on anticoagulants, has liver disease, etc.) 2
  • Be aware that different thromboplastin reagents may yield different results, especially in patients with liver disease 7, 5