Warfarin, Serum or Plasma

CPT: 80375
Print Share

Test Details

Synonyms

  • Coumadin®
  • Jantoven®
  • Sodium Warfarin

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.1,2

Limitations

Assay measures sodium warfarin only

Methodology

Liquid chromatography/tandem mass spectrometry (LC/MS-MS)

Reference Interval

1.0−10.0 μg/mL

Critical Value

Potentially toxic: >10.0 μg/mL

Additional Information

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 decline before maximal anticoagulation is reached. Warfarin is highly lipophilic and is 99% bound to albumin. Some tissue binding occurs, particularly in the liver; however, only the unbound drug is active and available for hydroxylation in the liver. Therefore, co-administered agents which either increase the free fraction (eg, salicylates) or activate liver enzymes (eg, St John's wort) need to be monitored cautiously.3

Specimen Requirements

Specimen

Serum or plasma

Volume

2 mL

Minimum Volume

0.6 mL

Container

Red-top tube, lavender-top (EDTA) tube, or green-top (heparin) tube. 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.

Collection

Transfer separated serum or plasma to a plastic transport tube.

Storage Instructions

Room temperature

Stability Requirements

Temperature

Period

Room temperature

14 days

Refrigerated

14 days

Frozen

14 days

Freeze/thaw cycles

Stable x3

Causes for Rejection

Gel-barrier tube

Clinical Information

Footnotes

1. Montamat SC, Cusack BJ, Vestal RE. Management of drug therapy in the elderly. N Engl J Med. 1989 Aug 3; 321(5):303-309. 2664519
2. James AH, Britt RP, Raskino CL, Thompson SG. Factors affecting the maintenance dose of warfarin. J Clin Pathol. 1992 Aug; 45(8):704-706. 1401182
3. Williamson EM. Drug interactions between herbal and prescription medicines. Drug Saf. 2003; 26(15):1075-1092 (review). 14640772

References

AMA, Division of Drugs and Toxicology. Drug Evaluations Subscription. Chicago, Ill: American Medical Association, Spring 1992.
Mosby's Drug Consult. St Louis, Mo: Elsevier Mosby; 2006.

LOINC® Map

Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
071423 Warfarin (Coumadin), Serum 4098-0 071424 Warfarin (Coumadin), Serum ug/mL 4098-0
Reflex Table for Warfarin (Coumadin), Serum
Order Code Order Name Result Code Result Name UofM Result LOINC
Reflex 1 007000 See below: 007000 See below: N/A

For Providers

Please login to order a test.

 

© 2017  Laboratory Corporation of America® Holdings and Lexi-Comp Inc. All Rights Reserved.

CPT Statement/Profile Statement

The LOINC® codes are copyright © 1994-2017, Regenstrief Institute, Inc. and the Logical Observation Identifiers Names and Codes (LOINC) Committee. Permission is granted in perpetuity, without payment of license fees or royalties, to use, copy, or distribute the LOINC® codes for any commercial or non-commercial purpose, subject to the terms under the license agreement found at https://loinc.org/license/. Additional information regarding LOINC® codes can be found at LOINC.org, including the LOINC Manual, which can be downloaded at LOINC.org/downloads/files/LOINCManual.pdf