Days Set Up
Daily, 24 hours
Analytic Time

STAT 1 hour, Routine 4 hours

MiChart Code
Soft Order Code

Test Updated:


International Normalized Ratio (INR)
Pro Time
Prothrombin Time
PT and INR

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Test Overview

Test Methodology

Photo-optical clot detection using recombinant thromboplastin.

Test Usage

The PT is sensitive to a factor VII deficiency and it is moderately sensitive to deficiencies of factors II, V, X and fibrinogen. The PT assay can also be used to determine, Warfarin (Coumadin) therapy, vitamin K deficiencies, liver disease, and intravascular coagulation syndrome (DIC).

Reference Range

9.3 - 12.0 seconds. Critical value: INR >5.0. Recommended therapeutic ranges for oral anticoagulant therapy: INR 1.2 - 1.5 Prevention of catheter-related venous thrombosis; INR 2.0 - 3.0 Treatment of venous or pulmonary embolism, prevention of systemic embolism, tissue heart valves, atrial fibrillation, valvular heart disease; INR 2.5 - 3.5 Mechanical prosthetic valves; INR >2.0 - 3.0 Certain patients with thrombosis and the antiphospholipid syndrome.

* Reference ranges may change over time. Please refer to the original patient report when evaluating results.

Specimen Requirements

Collection Offsite

Collect specimen in a blue top (citrate 3.2%) tube. Mix by inversion. Specimen should arrive at lab within 23 hours of collection; transport at room temperature. Alternatively, centrifuge, aliquot plasma into a plastic tube, and freeze the specimen within 4 hours of collection. Transport frozen specimen on dry ice. Collection of the blood through lines that have been previously flushed with heparin should be avoided. If the blood must be drawn through a VAD (vascular access device), the line should be flushed with 5 mL of saline and the first 5 mL of blood or six dead space volumes of the VAD discarded.

Blue Top Tube
Normal Volume
Full 2.7mL tube or 1mL plasma aliquot
Minimum Volume
Full 1.8mL tube or 1mL plasma aliquot

Billing Information

CPT Code
Pro Fee Code

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Our High Standard

Quality that sets us apart

As the reference laboratory division of Michigan Medicine's Department of Pathology, MLabs shares the institution's commitment to applying established quality principles to clinical laboratory testing. Like other large organizations in complex, consequential fields, we rely on an established approach to monitor quality throughout the testing process.