Prothrombin Time/International Normalized Ratio
Also known as: PT INR
Use
The Prothrombin Time/International Normalized Ratio (PT/INR) test is used primarily to evaluate bleeding disorders and to monitor oral anticoagulation therapy, such as warfarin (Coumadin). The INR is a standardized measure used to ensure consistent results across different laboratories and is critical for managing patients on anticoagulation therapy. This test aids in the prophylaxis of venous thromboembolism, treatment of venous thrombosis, prevention of systemic embolism, and is crucial for patients with mechanical prosthetic heart valves and recurrent systemic embolism.
Special Instructions
When submitting multiple tests, separate specimens should be provided for each test due to the critical frozen storage requirement. It is important to note that serum, EDTA plasma, clotted, or hemolyzed specimens are unacceptable for testing. Ensure the use of a Lt. blue (sodium citrate) collection tube, and immediately transfer 1 mL of platelet-poor plasma to an ARUP standard transport tube, keeping it in a critical frozen state until testing.
Limitations
The test is limited to evaluating patients specifically on oral anticoagulant therapy. The INR should not be used independently for diagnosis without consideration of clinical context and prior results. Variations in collection techniques or conditions could affect results, and room temperature stability is limited to 24 hours, with refrigerated specimens deemed unacceptable.
New York Approved
Methodology
Other
Biomarkers
LOINC Codes
- 5902-2
- 6301-6
Result Turnaround Time
1-2 days
Related Documents
For more information, please review the documents below
Specimen
Plasma
Volume
1 mL
Minimum Volume
0.5 mL
Container
ARUP standard transport tube
Collection Instructions
Collect using Lt. blue (sodium citrate) tube. Transfer 1 mL platelet-poor plasma to an ARUP standard transport tube.
Storage Instructions
CRITICAL FROZEN. Separate specimens must be submitted for multiple tests.
Causes for Rejection
Serum. EDTA plasma, clotted or hemolyzed specimens.
Stability Requirements
| Temperature | Period |
|---|---|
| Room Temperature | 24 hours |
| Refrigerated | Unacceptable |
| Frozen | 2 weeks |
Other tests from different labs that may be relevant