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Test Code PTIM Protime-INR, LAB320


Clot Based Assay

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:



≤16 years


>17 years



Day(s) Test Set Up

Monday through Sunday

Test Classification and CPT Coding


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.