Clinics and Departments

Laboratory Services

Lab Dept:

Coagulation

Test Name:

PROTIME AND INR (WARFARIN)

General Information

Lab Order Codes:

WPT

Synonyms:

PT; Protime; Prothrombin Time and INR for patients receiving oral anticoagulants, ie, Coumadin/Warfarin

CPT Codes:

85610 - Prothrombin time

Test Includes:

PT reported in seconds and INR

Logistics

Test Indications:

Useful for monitoring or adjusting the amount of Coumadin for a patient on oral anticoagulant therapy.

Lab Testing Sections:

Coagulation

Phone Numbers:

MIN Lab: 612-813-6280

STP Lab: 651-220-6550

Test Availability:

Daily, 24 hours

Turnaround Time:

2 hours

Special Instructions:

● Patient’s with hematocrit levels >55% must have a special tube made to adjust for the hematocrit; contact the laboratory for special tube.|
● Depending on the patient's hematocrit, up to 3 assays can be determined using one 1.8 mL light blue top tube.

Specimen

Specimen Type:

Whole blood

Container:

Light Blue top (Buffered Na Citrate 3.2%) tube

Draw Volume:

1.8 mL or 2.7 mL blood

Processed Volume:

1 mL (Minimum: 0.5 mL) plasma

Collection:

● A clean venipuncture is essential.
● Mix thoroughly by gentle inversion.
● Deliver immediately to the laboratory.

Special Processing:

Lab staff: Centrifuge in Stat Spin for 5 minutes or 10 minutes at 3000 rpm at room temperature. For primary tube testing, leave plasma on cells OR remove plasma and place in a 4 mL plastic cup; allow for 100 uL of deadspace.

Test within:
● Twenty-four (24) hours when stored as plasma remaining in the capped tube above the packed cells 18 to 24C.
● Four (4) hours as plasma that has been separated from cells by centrifugation when stored 2 to 8C or 18 to 24C.
● Two (2) weeks when stored -20C.
● Six (6) months when stored -70C (rapidly frozen).
● Plasma must be frozen if testing cannot be completed within four (4) hours.
● Frozen plasmas are thawed at 37C for three (3) minutes, test immediately.

Patient Preparation:

None

Sample Rejection:

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

Interpretive

Reference Range:

Test

All ages

INR Therapeutic Ranges for Oral Anticoagulants

Prophylactic dose:

1.4 – 1.9

Standard dose:

2.0 – 3.0

High dose:

2.5 – 3.5

Note: Extremely high results will be reported as PT >120.0, INR >9.0

Critical Values:

INR: <1.4 or >3.5

Methodology:

Recombinant human tissue factor combined with synthetic phospholipids (thromboplastin)

References:

Harmening DH (1997) Clinical Hematology and Fundamentals of Hemostasis

Updates:

8/19/2013: Updated specimen stability information.
12/18/2013: Updated specimen stability information.



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