Prothrombin Time and International Normalized Ratio (PT/INR) CPT: 85610

Expected Turnaround Time

Within 1 day

Specimen Requirements




1 mL

Minimum Volume

0.5 mL


Light-blue top (3.2% sodium citrate)


1. Centrifuge, remove plasma, and centrifuge plasma again.

2. Aliquot plasma into plastic vial leaving 0.25 mL in the bottom of centrifuged vial.

Additional Information: Double-centrifuged specimen is critical for accurate results as platelet contamination may cause spurious results.

Storage Instructions

Maintain specimen at room temperature.

Stability Requirements

Temperature Period
Room Temperature3 Days
Refrigerated3 Days
Frozen2 Months
Freeze/thaw/ cycles X 3

Patient Information

A prothrombin time (PT) is a test used to help detect and diagnose a bleeding disorder or excessive clotting disorder; the international normalized ratio (INR) is calculated from a PT result and is used to monitor how well the blood-thinning medication (anticoagulant) warfarin (Coumadin®) is working to prevent blood clots.

When you are taking warfarin or when you have unexplained or prolonged bleeding or inappropriate blood clotting.

A blood sample drawn from a vein; sometimes blood from a fingerstick.

None needed, although if you are receiving anticoagulant therapy, the blood sample should be collected before taking your daily dose.