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Test Code PTIM Protime-INR, LAB320

Performing Laboratory

St. Luke's Hospital Cedar Rapids

Specimen Requirements


Preferred: Full Blue-top (sodium citrate) tube (1.8mL)-Hemolyzed or short draw specimen is not acceptable.
Volume: 0.5 mL sodium citrate plasma

Stability: Uncentrifuged or centrifuged in an unopened tube kept at 18-24°C must be tested within 24 hours from the time of specimen collection.  If testing is not completed within 24 hours, plasma should be removed from the cells and frozen at -20°C for up to two weeks.

NOTE:  Patients with a hematocrit of >55% must be recollected using an altered amount of sodium citrate.

Reference Values

PT: 9.3-11.7 seconds


Normal: 0.9-1.1

Critical value: INR ≥5.0

Useful For

The prothrombin time (PT) and calculated international normalized ratio (INR) is a useful screening procedure for deficiencies in factors II, V, VII, and X.  This test may be used to follow the course of anticoagulant therapy in patients receiving Coumadin drugs. 

Day(s) Test Set Up

Monday through Sunday


Clot Based Assay

Test Classification and CPT Coding