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HelpTest Code LAB3553 Warfarin Prothrombin Time + INR
Clinical System Name
Warfarin Prothrombin Time + INR
Description
The Warfarin PT test is used to monitor patients receiving Warfarin therapy.
Sample Requirements
Specimen: Whole Blood
Container(s): Lt Blue/Citrate
Required Vol: (1) 1.8 mL or (1) 2.7 mL
Minimum Vol: N
Note: This is enough for a Warfarin PT, PTT, TT, and Fibrinogen to be run on the same sample.
Preferred method of collection is venipuncture with vacuum fill. Test results are affected by incorrect blood volume. Use of a Vascular Access Device for the collection of coag testing is not recommended. Please review the Coagulation Lab Collection Job Aid for detailed instructions.
Processing Instructions: Main Campus
Deliver whole blood to Coag bench. Coag Technologist will process.
Reject due to: clotted, insufficient quantity (underfill), or improper collection (overfill).
Spin: Y
Aliquot: Y
Storage location: Core 14 Freezer ( -70 C).
Specimen should be centrifuged within one hour of collection. Transfer upper 3/4 layer of plasma to plastic tube affixed with large Epic aliquot label. Do not pool. Assay immediately.
Processing Instructions: Offsite & Regional Clinics
Reject due to: clotted, insufficient quantity (underfill), or improper collection (overfill).
Spin: Y
Aliquot: Y
Storage location: -70 C (preferred) or -20 C.
Specimen should be centrifuged within one hour of collection. Double spin, transfer upper 3/4 layer of plasma to plastic tube affixed with large sample label. Freeze one aliquot of plasma at -70 C (preferred) or -20 C. Preferred plasma volume: 1.0 mL, minimum plasma volume: 0.6 mL. Do not pool.
Non-Children's Hospital Offsite collection: Ship completely frozen on dry ice.
Children's Hospital Regional Clinic collection: Ship completely frozen in frozen Nalgene Labtop cooler with ice pack inside an insulated soft cooler.
Stability
| Specimen Type | Temperature | Time |
|---|---|---|
| Citrated platelet-poor plasma | Room temp | ≤4 h |
| Refrigerated | N | |
| Frozen -20 C or -70 C | ≤3 m |
Performing Laboratory
Seattle Children's Laboratory
Department
Department: Coagulation
Phone Number: 206 987-2617 (Client Services)
Synonyms
LAB3553
WARF PT
INR
Protime
PT
PT INR
Availability
| STAT | Performed | TAT |
|---|---|---|
| Y |
Daily |
1 h |
Methodology
Method: Electromagnetic mechanical clot detection assay by STA-R MAX
Analytical Volume: 100 uL plasma
Limitations: Method is affected by insufficient quantity (underfill), improper collection (overfill), improper processing, and improper storage. High hematocrit greater than or equal to 56% requires a citrate adjusted tube.
The PT/INR shows variable prolongations in patients on direct thrombin inhibitors argatroban and bivalirudin, and should not be used to monitor coagulation factor levels. To monitor coagulation factors in patients on direct thrombin inhibitors please order Factor 10 Assay, Chromogenic (LAB3030).
Reference Range
Reference range determined by provider.
CPT Codes
85610
Critical Values
| Critical INR | Critial PT |
| Less than or equal to 1.5 or greater than or equal to 4.0 | >39.2 s |