Clinics and Departments

Laboratory Services

Lab Dept:

Coagulation

Test Name:

PROTIME AND INR

General Information

Lab Order Codes:

PT

Synonyms:

PT; Protime; Prothrombin Time and INR

CPT Codes:

85610 - Prothrombin time

Test Includes:

PT reported in seconds and INR

Logistics

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.

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, avoid foaming.
● Entire sample must be collected with single collection, pooling of sample is unacceptable.
● Capillary collection is unacceptable.
● Patient’s with a hematocrit level >55% must have a special tube made to adjust for the hematocrit; contact lab for a special tube.
● Mix thoroughly by gentle inversion. Deliver immediately to the laboratory at room temperature via courier or pneumatic tube.

Off campus collections:
● Must be tested within 24 hours.
● Do not refrigerate.
● If not received in our lab within 24 hours of collection, sample must be centrifuged and *platelet-poor plasma removed from cells and transferred to an aliquot tube. Freeze at -20C and deliver to the lab on dry ice within 2 weeks.
*Validation of your lab’s centrifuge for platelet poor plasma is required.

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

PT:

8.5 – 12.4 seconds

INR:

0.79 – 1.20

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:

PT: >17.0 seconds

INR: >1.7

Limitations:

N/A

Methodology:

Placental Thromboplastin

References:

Harmening DH (1997) Clinical Hematology and Fundamentals of Hemostasis

Updates:

2/17/2005: Critical value for INR previously listed as >1.5.
7/19/2006: Removed statement, "Do not transport by pneumatic tube".
7/25/2006: Added Oral Anticoagulant therapeutic ranges.
1/30/2008: Edited reference ranges: PT previously reported as: 10.6 – 15.5 seconds, critical value previously reported as: >21.2
8/19/2013: Updated specimen stability information.
9/25/2014: Added Off Campus collection info.



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