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
- Blood
- 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
- Receiving Instructions
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
- Misc Sendout
Performance
- Lab Department
- Coagulation(COAG)
- Frequency
- Daily
- Available STAT?
- Yes
- Performing Location(s)
-
HMC Coagulation
206-520-4600325 9th Ave, Rm # GWH-47, Seattle, WA 98104-2420
UW-NW Main Lab
206-668-1344UW Medical Center – Northwest
1550 N 115th Street, A200
Seattle, WA 98133FHCC Fred Hutch Alliance Lab
206-606-1088825 Eastlake Ave, Seattle, WA 98109
UW-MT Coagulation
206-520-4600Clinical Lab, Room NW220,
University of Washington Medical Center,
1959 NE Pacific street, Seattle, WA 98195
Billing & Coding
- CPT Codes
- 85610
- LOINC
- 34528-0
- Interfaced Order Code
- UOW2559