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Test ID WRF Warfarin, Serum

Useful For

Monitoring patients whose prothrombin time is inconsistent with the prescribed warfarin dose, particularly when failure to comply or surreptitious drug use is suspected.

Note: This test is not useful for evaluation of the patient with prolonged bleeding time suspected of exposure to rat poisons.

Method Name

High-Performance Liquid Chromatography (HPLC)

Reporting Name

Warfarin, S

Specimen Type

Serum Red

Container/Tube: Red top

Specimen Volume: 3 mL

Collection Instructions: Spin down within 2 hours of draw.

Forms: If not ordering electronically, complete, print, and send a Cardiovascular Test Request Form (T724) with the specimen (http://www.mayomedicallaboratories.com/it-mmfiles/cardiovascular-request-form.pdf).

Specimen Minimum Volume

1.1 mL

Specimen Stability Information

Specimen Type Temperature Time
Serum Red Refrigerated (preferred) 21 days
  Ambient  28 days
  Frozen  28 days

Clinical Information

Warfarin (Coumadin) is an anticoagulant that acts by antagonizing the action of vitamin K resulting in the same coagulation abnormalities produced by vitamin K deficiency.

 

Warfarin reduces the levels of prothrombin and factors VII, IX, and X, thereby prolonging the prothrombin and partial thromboplastin times.

 

Warfarin produces its anticoagulant effect within 36 to 72 hours of initiating therapy, and the duration of action may persist for 4 to 5 days following withdrawal of drug.

 

Warfarin circulates almost completely bound to albumin (>98%), and its half-life ranges from 20 to 60 hours.

 

Abnormal bleeding is the chief complication of overdose.

Reference Values

Therapeutic concentration: 2.0-5.0 mcg/mL

Toxic concentration: ≥10.0 mcg/mL

Cautions

This test is not useful for evaluation of the patient with prolonged bleeding who are suspected of exposure to rat poisons.

 

Patients transfused with fresh-frozen plasma may have a disparity between their warfarin level (elevated) and a relatively normal prothrombin.

Day(s) Performed

Wednesday; 4 p.m.

Report Available

2 days

Performing Laboratory

Mayo Medical Laboratories in Rochester

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

CPT Code Information

80299

NY State Approved

Yes