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Test Code LAB320 Prothrombin Time (PT), Plasma

Important Note

Direct oral anticoagulants which inhibit Factor Xa (rivaroxaban, apixaban, edoxaban) positively interfere with the PT/INR (e.g. anti-Xa DOACs prescribed concurrently with warfarin/Coumadin can produce a falsely elevated PT/INR).

Performing Laboratory

Barnes-Jewish Hospital Laboratory

Methodology

Absorbance measurement, Clot signature formation
Includes international normalized ratio (INR).
Literature References:
Package insert: RecombiPlasTin 2G determination of prothrombin time by ACL TOP, Instrumentation Laboratory, 11/2014.

Specimen Requirements

Specimen Type: Plasma

Container/Tube: Light-blue top (citrate)
Specimen Volume: Full tube
Specimen Minimum Volume: Full tube
Collection Instructions:

  1. Draw a discard blue top tube prior to drawing a light-blue top (citrated) tube if using a Winged Infusion Set.  Discard tube should be under filled and discarded.
  2. Clotted blood or an insufficient specimen is not acceptable.
  3. Avoid phlebotomy techniques which cause hemolysis and heparin contamination.
  4. Follow nursing policy on volume of blood to discard prior to collecting blood from indwelling heparinized catheters.

Analyte Stability:

24 hours at 2° C to 24° C

Additional Information: If the patient is a hospital patient and the hematocrit is >55%, call Barnes-Jewish Hematology Laboratory at 314-362-5203 for instructions.

Day(s) Test Set Up

Monday through Sunday

Turnaround Time:

STAT: 1 hour after receipt in laboratory

Routine: 2-4 hours after receipt in laboratory

Test Classification and CPT Coding

85610

Reference Values

PT
9.7 -13.0 seconds


INR
0.90 - 1.20
Physician alert value (automatic call-back): >5.0 INR

Specimen Transport Temperature

Ambient/Refrigerate NO/Frozen NO

Additional Information

For BJH Laboratory Use Only
Analyte Stability:

24 hours at 2° C to 24° C

Laboratory Processing Instructions:

Test performed in BJH Core Lab.

LOINC Code Information

Name LOINC Code
Prothrombin Time 5902-2
INR 6301-6