Lab Dept:


Test Name:


General Information

Lab Order Codes:



Protime to U of M; Prothrombin Time to U of M; PT to U of M; International Normalized Ratio; INR

CPT Codes:

85610 - Prothrombin time

Test Includes:

INR; Protime (PT) is Not reported


Test Indications:

Useful for evaluating the extrinsic and common pathways of the coagulation system; aid in screening for congenital deficiencies of factors II, V, VII, and X, dysfibrinogenemia, afibrinogenemia, coumarin effect, liver disease, disseminated intravascular coagulation (DIC), and vitamin K deficiency.

The International Normalized Ratio (INR) is now the most widely recommended test for monitoring oral anticoagulation because the INR, unlike the prothrombin time (PT) reported in seconds, is largely independent of the specific instrument and reagent used.

Lab Testing Section:

Coagulation - Sendouts

Referred to:

Fairview University Medical Center

Phone Numbers:

MIN Lab: 612-813-6280

STP Lab: 651-220-6550

Test Availability:

Daily, 24 hours

Turnaround Time:

8 hours routine

Special Instructions:

Patient should not be receiving Coumadin® or heparin. If so, this should be noted on the request form. Heparin or warfarin therapy can affect certain coagulation factors or assays, preclude their performance, or cause spurious results.

Indicate when specimen is drawn from a line or a heparin lock. Deliver immediately to the laboratory.


Specimen Type:

Whole blood


Light Blue top (Buffered Na Citrate 3.2%) tube

Draw Volume:

2.7 mL blood in a 3 mL tube (Minimum: 2.7 mL in a 3 mL tube)

Processed Volume:

Specimens will be processed at reference lab facility if received within 4 hours of collection. Otherwise, specimens need to be processed at referring facility and provide minimum of two 0.5 mL specimens frozen at -70. Follow directions below under Special Processing.


Patients with hematocrit levels >55% must have a special tube made to adjust for the hematocrit, contact laboratory for special tube.

Fill tube completely. Mix thoroughly by gentle inversion.


Special Processing:

Lab Staff: Do Not centrifuge. Do Not freeze. Send to reference lab in original Vacutainer® at room temperature if within 4 hours of collection. Forward promptly.

If specimen is >4 hours old prior to shipment, process specimen as follows: Spin sample collected in blue top tube(s) for 5 minutes on the Stat Spin centrifuge, remove plasma and transfer to a 4 mL BCS sample cup(s), spin remaining plasma again for 5 minutes in the Stat Spin Centrifuge. Transfer plasma into two labeled 10x75 mL plastic tubes with a minimum of 0.5 mL in each. Freeze at -70 and send specimens on dry ice to Fairview University.

Patient Preparation:


Sample Rejection:

Improper tube; clotted specimen; underfilled tubes; overfilled tubes; mislabeled or unlabeled specimens


Reference Range:



0 – 1 month:

0.81 – 1.30

1 – 6 months:

0.81 – 1.17

> 6 months:

0.86 – 1.14

Critical Values:



Increased in patients taking oral contraceptives


Quick One Stage Prothrombin Time


Fairview University Medical Center Laboratory Web Page February 2014

Harmening DH (1997) Clinical Hematology and Fundamentals of Hemostasis


6/3/2004: Reference ranges changed from one range of >1 year: 0.85 – 1.15 to the expanded ranges by age listed under Reference Range:
Draw volume was updated from 4.5 mL to 2.7 mL blood.
5/25/2010: Tubing patient specimens is no longer prohibited.
2/25/2014: Fairview updated specimen processing instructions.