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Test Code PTINR Prothrombin Time (PT), Plasma

Important Note

Useful for:

Monitoring of intensity of oral anticoagulant (Coumadin(R)) therapy when combined with INR

Screening assay to detect deficiencies of one or more coagulation factors

Screening assay to detect coagulation inhibition

Specimen Requirements

Citrated Plasma

Collect blood in a blue-top 0.109M (3.2%) buffered sodium citrate tube. Invert several times to mix blood. Label the specimen with the patient's name (first and last), date of birth, date and time of collection and the phlebotomist's initials. Send sodium citrate whole blood in the original VACUTAINER®. Forward unprocessed whole blood promptly to the lab. 

 

 If there is a delay in transport of ≥24 hours, process specimen as follows:

 

Centrifuge specimen for 10 minutes at 3,000 rpm, remove plasma, and place 0.5 mL of sodium citrate plasma in plastic vial. (Glass vial is not acceptable.) Send specimen frozen in plastic vial.

 

Specimen Stability

24 hours when kept at room temperature, unopened, spun or unspun.

If testing cannot be completed within 24 hours separate plasma and freeze specimen at ≤ -20°C for up to 2 weeks.

 

Separated plasma may be stored for 8 hours at 18 - 24°C. 

If testing cannot be completed within 8 hours freeze specimen at ≤ -20°C for up to 2 weeks

 

Minimum Volume

The proportion of blood to anticoagulant volume must be 9:1.

Specimen tube must be filled to at least 90% of capacity of the collection tube. Fill to the line indicated on the tube. 

Reference Values

INTERNATIONAL NORMALIZED RATIO (INR)

Normal range:   0.8-1.2

Therapeutic range:  2.0-3.0 (standard therapy)

Critical value (automatic call-back):  >4.0

Day(s) Test Performed

Monday - Sunday

Performing Laboratory

MaineGeneral Medical Center

Test Classification and CPT Coding

85610