Prothrombin Time and International Normalized Ratio


Core Lab Study

Protime, PT, and INR.

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

A small group of studies in this manual have been identified as Core Lab Studies. The designation is meant to assist the reader in sorting the basic “always need to know” laboratory studies from the hundreds of other valuable studies found in the manual—a way to begin putting it all together.

Normal, abnormal, or various combinations of core lab study results can indicate that all is well, reveal a problem that requires further investigation with additional testing, signal a positive response to treatment, or suggest that the health status is as expected for the associated situation and time frame.

Prothrombin time (PT)/international normalized ratio (INR) is a frequently requested test used to monitor patients at risk for developing blood clots, heart attack, or stroke; especially those who receive treatment with warfarin, an oral vitamin K antagonist. Warfarin is an effective medication, but it must be closely monitored due to a significant risk for bleeding.Patient Preparation
There are no food, fluid, activity, or medication restrictions unless by medical direction.

Normal Findings
(Method: Clot detection)

AgeConventional Units
Newborn10.2–15.4 sec
1 wk–6 mo9.9–13.6 sec
7 mo–17 yr9.7–12.3 sec
Adult10–13 sec
  • INR = 0.9 to 1.1 for patients not receiving anticoagulation therapy. Values may be slightly higher in newborns and children less than 1 yr.
  • 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 InterventionsINR

  • 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/INR is within the expected range. Intramuscular (IM) administration of vitamin K, an anticoagulant reversal drug, may be requested by the HCP.

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