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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

Specimen Required

Container/Tube: Red top

Specimen Volume: 3 mL

Collection Instructions: Spin down within 2 hours of draw.

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

Reference Values

Therapeutic concentration: 2.0-5.0 mcg/mL

Toxic concentration: ≥10.0 mcg/mL

Day(s) and Time(s) Performed

Tuesday; 11 a.m.

Performing Laboratory

Mayo Clinic Laboratories in Rochester

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
WRF Warfarin, S 4098-0


Result ID Test Result Name Result LOINC Value
8760 Warfarin, S 4098-0

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.


If not ordering electronically, complete, print, and send a Cardiovascular Test Request Form (T724) with the specimen.