Understanding Your Coagulation Test Results
Your results are completely normal and indicate that your blood clotting system is functioning properly. 1
What Each Test Measures
PT (Prothrombin Time) - 13.0 seconds
- Your result: 13.0 seconds is within the normal range of 11.5-14.5 seconds 1
- PT evaluates the extrinsic and common coagulation pathways, specifically measuring factors II, V, VII, X, and fibrinogen 2, 3
- This test is primarily designed to monitor patients taking warfarin (vitamin K antagonist therapy) 2, 4
INR (International Normalized Ratio) - 1.0
- Your result: 1.0 is normal (healthy individuals not on anticoagulation typically range 0.8-1.2) 1
- The INR standardizes PT results across different laboratories using the formula: INR = (PT patient/PT normal)^ISI, where ISI is the international sensitivity index specific to each thromboplastin reagent 1, 5
- The INR scale is only valid and meaningful for patients taking warfarin - it should not be interpreted as a general screening test in patients not on vitamin K antagonists 2, 1, 6
- For patients on warfarin therapy, the therapeutic INR range is typically 2.0-3.0 1, 4
PTT (Partial Thromboplastin Time) - 31.0 seconds
- Your result: 31.0 seconds is normal (typical reference ranges vary by laboratory but generally 25-35 seconds) 3
- PTT evaluates the intrinsic and common coagulation pathways, measuring factors VIII, IX, XI, XII, and the common pathway factors 3, 7
- This test is primarily used to monitor unfractionated heparin therapy 3, 7
Clinical Interpretation
Since you are not on anticoagulation therapy (based on your normal values), no intervention is required 1
- Your normal PT indicates adequate levels of clotting factors in the extrinsic and common pathways 3
- Your normal PTT indicates adequate levels of clotting factors in the intrinsic and common pathways 3
- These results effectively rule out significant deficiencies in vitamin K-dependent factors (II, VII, IX, X), liver dysfunction affecting coagulation factor synthesis, and consumption coagulopathies like DIC 2, 3
Important Caveats
- Do not use INR as a general screening test - the INR was specifically designed and validated only for monitoring warfarin therapy, not as a predictor of bleeding risk in non-anticoagulated patients 2, 6
- If bleeding occurs despite normal PT/PTT, investigate for platelet disorders, factor XIII deficiency, or vascular abnormalities 7
- Normal PT and PTT do NOT exclude the presence of direct oral anticoagulants (DOACs) like rivaroxaban, apixaban, or dabigatran 7