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 Field Name  Data Description
Test Name  Warfarin
Code  Warfarin (Coumadin), Serum.
CPT Code  80375
Last Modified  7/11/2018 10:51:00 AM
Test Name  Coumadin.
Synonyms  Coumadin, Jantoven, Sodium Warfarin
Patient Preparation  
Spec. Requirements  Blood
Tube  Red, Lavender(EDTA) or Dark Green(Heparin)
Collection Volume  4.0 mL Red, 2.0 mL Lavender or 4.0 mL Dark Green
Storage  Ambient, Refrigerated or Frozen 14 Days
Routine TAT  
Days Test Performed  
Performed by BHS  None
See Availability  
Reference Lab  LabCorp of America
Reference Lab Code  071423 Warfarin (Coumadin), Serum
Clinical Use  Warfarin is used for chronic oral anticoagulation in a variety of clinical settings. Management of warfarin therapy is usually by following the PROTHROMBIN TIME, rather than by measuring serum drug concentrations. Warfarin is subject to a bewildering number and variety of drug interactions, producing increased or decreased clinical effect of itself or other drugs. Many of these effects are due to changes in protein binding or hepatic metabolism. Reductions in dosage may be indicated for aging subjects treated for venous thromboembolic or coronary arterial disease, but not in those with peripheral vascular disease, deep vein thrombosis, or valvular heart disease. Warfarin is intermediate acting: a peak effect is achieved in 36 to 72 hours and the anticoagulant effect persists for two to five days. The drug is rapidly and completely absorbed from the gastrointestinal tract. The delay in achieving the peak effect results from the long half-lives of clotting factors II, IX, and X, whose levels must declinebefore maximal anticoagulation is reached. Warfarin is highly lipophilic and is 99% bound to albumin. Some tissue binding occurs, particularly in the liver; however, only theunbound drug is active and available for hydroxylation in the liver. Therefore, co-administrated agents which either increase the free fraction (eg, salicylates) or activate liver enzymes (eg, St John's wort) need to be monitored cautiously.
Reference Range  1.0-10.0 mg/mL
Critical Value  Potentially toxic: >10.0 mg/mL
Reference Range  
Critical Value  
Testing Sample Type  Serum or Plasma
Min Lab Testing Volume  0.6 mL
Special Handling  DO NOT USE A GEL-BARRIER TUBE. The use of gel-barrier tubes is not recommended due to slow absorption of the drug by the gel. Depending on the specimen volume and storage time, the decrease in drug level due to absorption may be clinically significant.
Lab Notes  Collection: Transfer separated serum or plasma to a plastic transport tube. Causes for rejection: Gel-barrier tube
Methodology  LC/MS-MS - Liquid Chromatography/Tandem Mass Spectrometry
Limitations  Assay measures sodium warfarin only

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