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Test Code APTHR Prothrombin (PT) with INR, Plasma

Additional Codes

EPIC:  LAB320

Methodology

Chromogenic


Used in monitoring oral anticoagulation therapy.

Performing Laboratory

St. Joseph Hospital

Specimen Requirements

Collect a full, light blue-top (3.2% sodium citrate) tube. (Hemolyzed specimen is not acceptable.) Centrifuge at 2,500 rpm for 15 minutes or 3,000 rpm for 10 minutes.  centrifuged specimen is good for 8 hours at ambient temp. Do not refrigerate. 

Reference Values

PT

12.1 - 13.9 seconds (without anticoagulant therapy)

INR

0.9 - 1.1 (normal)

2.0-3.0 (therapeutic)

Critical value:  ≥ 5.0

Note:  Values may vary with reagent lot changes. Always refer to patient report for current range.

Day(s) Test Set Up

Monday through Sunday

Available STAT

Test Classification and CPT Coding

85610

Clinical Significance

The prothrombin time is a general screening procedure for the detection of deficiencies of clotting factors in the extrinsic system (Factors II, V VII and IX).  Its major use, however, is in monitoring oral anticoagulant therapy.  The oral anticoagulant coumadin depresses the liver’s production of Factors II, VII, XI and X by reducing the availability of vitamin K.  Since the prothrombin time is most sensitive for Factors VII and X, it can be used to monitor the effects of the drug.  The results are reported in seconds and INR to allow physicians to manage pre-operative patients, patients undergoing coumadin therapy for a variety of reasons and patients undergoing coumadin induction therapy.