Prothrombin Time
General Information
Lab Name
Prothrombin Time
Lab Code
PRO
Epic Name
Prothrombin Time
Description
The prothrombin time is a coagulation sceening test to measure the activity of the coagulation factors II, V, VII, X and I. Prothrombin time (INR) can be used to monitor anticoagulation therapy with warfarin. For information regarding the use of this test for anticoagulant monitoring, visit UW Medicine Anticoagulation Services
Synonyms
INR, Protime
Components
| Code | Name |
|---|---|
| PROPAT | Prothrombin Time Patient |
| PROINR | Prothrombin INR |
Interpretation
Method
Clot based
Reference Range
See individual components
Ref. Range Notes
Critical Prothrombin time is the PT that generates an INR of 5.0 or higher.
Warfarin Therapy:
INR 2-3: For stroke prevention in atrial fibrillation; mechanical aortic valve replacement; prevention and treatment of venous thromboembolism
INR 2.5-3.5: For mechanical mitral valve replacement or recurrent venous or arterial thrombosis despite therapeutic anticoagulation. For more information, see web link above labeled “UW Medicine Anticoagulation Service”.
Interferences and Limitations
This assay is insensitive to unfractionated heparin levels up to 1 IU/ml and low molecular weight heparin levels up to 1.5 anti-Xa IU/mL. Thrombin inhibitors (argatroban, bivalirudin, etc.) present in the sample may lead to a prolonged prothrombin time. Prothrombin time may be prolonged in patients with high levels of direct factor Xa inhibitor drugs (such as rivaroxaban, apixaban, or edoxaban).
Ordering & Collection
Specimen Type
Collection
3 or 5 mL BLUE TOP (CITRATE) tube
Pediatric draws: (At UW-MT ONLY) Contact the lab at 206-598-6242 and ask for a baby draw tube for coagulation testing.
Handling Instructions
UW-MT/HMC/UW-NW: Laboratory MUST process the specimen within 24 hours of blood collection.
FHCC: Specimens must be processed within 8 hours of collection
Note: Stability studies apply to Protime only. Specimens for other coag testing must be processed within 4-6 hours depending on the test.
Quantity
requested: Entire sample
Processing
Take specimen to COAG lab.
Outside Laboratory: Whole blood samples for Prothrombin (INR) only are stable at room temperature for 24 hours in original capped tube. If other coagulation tests are ordered along with the Prothrombin (INR), then centrifuge sample for 10 minutes, remove plasma and re-spin plasma for another 10 minutes. Decant and freeze plasma (minimum 1.0 mL) at -20°C to -80°C. Send Frozen on dry ice.
Stability: Plasma samples frozen at -70°C or below are good for 1 year
Performance
LIS Dept Code
Coagulation (COAG)
Performing Location(s)
| HMC |
Coagulation
206-520-4600 325 9th Ave, Rm # GWH-47, Seattle, WA 98104-2420 |
|
|---|---|---|
| UW-NW |
Main Lab
206-668-1344 UW Medical Center – Northwest |
|
| FHCC |
Fred Hutch Alliance Lab
206-606-1088 825 Eastlake Ave, Seattle, WA 98109 |
|
| UW-MT |
Coagulation
206-520-4600 Clinical Lab, Room NW220, |
Frequency
Daily
Available STAT?
Yes