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Test Code LAB320 Protime - INR

Clinical Information

The PT is sensitive to a factor VII deficiency and it is moderately sensitive to deficiencies of factors II, V, X and fibrinogen. The PT assay can also be used to determine, Warfarin (Coumadin) therapy, vitamin K deficiencies, liver disease, and intravascular coagulation syndrome (DIC).

Synonym

  • PTI
  • PT/INR
  • Protime/INR

Specimen Required

Preferred Container/Tube: 3.2% Citrate Blue Top - 2.7 mL
Specimen Volume: 2.7 mL
Acceptable Container/Tube: 3.2% Citrate Blue Top - 1.8 mL
Specimen Volume: 1.8 mL
Platelet poor plasma (PPP):
Specimen Volume: 2 - 1 mL aliquots platelet poor plasma (PPP)
Specimen Minimum Volume: 1 - 1 mL aliquot platelet poor plasma (PPP)

Specimen Collection Information

For Outreach, other than OSU Patient Service Centers: Samples must be processed and received frozen/must remain frozen in transit. 

For sending frozen plasma specimens, process immediately upon receipt. Centrifuge capped specimen tube in accordance with CLSI H21, at a speed and time required to consistently produce platelet-poor plasma (PPP = platelet count <10 K/uL). Transfer PPP into plastic aliquot tubes, cap and freeze. DO NOT transport until specimens are completely frozen.

Specimen Stability Information

Ambient: 
     Capped whole blood: 24 hours
     Capped and centrifuged: 24 hours
     Uncapped whole blood: 8 hours
     Plasma: 8 hours
Frozen: 
      Platelet poor plasma: PPP removed from the cells and frozen at -20°C or ideally -70°C.

Rejection Due To

  • Ambient capped WB specimens >24 hours old
  • Ambient uncapped WB specimens >24 hours old
  • Ambient PPP specimens >8 hours old
  • Clotted specimens
  • Underfilled or overfilled tube
  • Hemolysis

Reference Values

PT
11.9-14.2 sec

 

INR
0.9-1.1

Cautions

A large number of drugs can interfere with the action of warfarin in vivo, either potentiating or inhibiting its effect on the coagulation factors II, VII, IX, and X. The Prothrombin Time is insensitive to unfractionated heparin up to approximately 2.0 units per mL. Inhibitors such as the lupus anticoagulant may interfere with Prothrombin Times. Direct thrombin inhibitors (Argatroban, Bivalarudin, etc) in therapeutic doses will result in prolonged Prothrombin Times. Patients with abnormally elevated hematocrits may show falsely prolonged PT.

Method Description

PT

Mechanical clot detection initiated by Calcium Thromboplastin

 

INR

Calculation

Performing Lab

Clinical Lab UH
Clinical Lab University East
Clinical Lab James
Clinical Lab Martha Morehouse
Clinical Lab Spielman
Clinical Lab West Campus

Day(s) Performed

Monday through Sunday

Report Available

Same day/1 day

Reporting Name

PT/INR

CPT Code Information

85610

LOINC Code Information

5902-2
34714-6