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Test Code WRF Warfarin, Serum

Reporting Name

Warfarin, S

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)

Performing Laboratory

Mayo Clinic Laboratories in Rochester

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

Reject Due To


Mild OK; Gross OK


Mild reject; Gross reject


Mild OK; Gross OK


Serum gel tube


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.

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


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


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