Prothrombin Time and International Normalized Ratio

Prothrombin Time and International Normalized Ratio is a topic covered in the Davis's Lab & Diagnostic Tests.

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Protime, PT, and INR.

To assess and monitor coagulation status related to therapeutic interventions and disorders such as vitamin K deficiency.

Patient Preparation
There are no food, fluid, activity, or medication restrictions unless by medical direction.

Normal Findings
(Method: Clot detection) 10 to 13 sec.

  • International normalized ratio (INR) = 0.9 to 1.1 for patients not receiving anticoagulation therapy.
  • INR = 2 to 3 for patients receiving conventional anticoagulation therapy with warfarin.
  • INR = 2.5 to 3.5 for patients receiving intensive anticoagulation therapy with warfarin.

Critical Findings and Potential Interventions


  • Greater than 5

Prothrombin Time

  • Greater than 27 sec

Timely notification to the requesting health-care provider (HCP) of any critical findings and related symptoms is a role expectation of the professional nurse. A listing of these findings varies among facilities.

Consideration may be given to verification of critical findings before action is taken. Policies vary among facilities and may include requesting immediate recollection and retesting by the laboratory or retesting using a rapid point-of-care testing instrument at the bedside, if available.

Important signs to note relate to bleeding in specific areas of the body and include prolonged bleeding from cuts or gums, hematoma at a puncture site, hemorrhage, blood in the stool, backache or flank pain, dark-colored urine, joint pain, persistent epistaxis, heavy or prolonged menstrual flow, and shock. Monitor vital signs, unusual ecchymosis, occult blood, severe headache, unusual dizziness, and neurological changes until PT is within normal range. Intramuscular (IM) administration of vitamin K, an anticoagulant reversal drug, may be requested by the HCP.

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