Arixtra (Fondaparinux) Assay


Abbrev Code:ARIX   
Order Code:LAB3292Order Name:Arixtra Level
Synonyms:Fondaparinux Assay
Methodology:Xa assay for Arixta
CPT Codes: 85520 x1, 85520 x1
Turnaround Time:Testing is performed as needed; results are reported within 8 hours if received into the testing laboratory by 12 p.m. For urgent testing after hours call 612-273-5551 to contact the tech on call.
Special Instructions:See link to Specimen Collection and Processing for Coagulation Specimens.
Associated Links:

Specimen Collection and Processing for Coagulation Specimens



Collection Instructions

Specimen:Blood
Optimal Volume:2.7 mL (in 3 mL tube) - filled to fill line on the tube.
Minimum\Peds Volume:1.8 mL (in 2 mL tube) - filled to fill line on the tube.
Container:Blue Na Citrate, 3.2% - fill to fill line on tube
Collection Instructions:See link to Specimen Collection and Processing for Coagulation Specimens.
Causes for Rejection:Underfilled tubes, overfilled tubes, clotted specimens, not received or processed and frozen within 4 hours of collection or, specimen thawed during transit.


Processing and Shipping

Specimen Processing:
  • Process for Platelet Poor Plasma within 4 hours of collection.
  • Aliquot plasma, place clear tape around label, and freeze at -20C or on dry ice within 4 hours of collection.
  • If multiple tests are collected on 1 blue top, split each blue top into 2 aliquots. Minimum 0.5 mL per tube.
  • A maximum of 6 aliquots are needed per collection.
     
See link to Specimen Collection and Processing for Coagulation Specimens.
Shipping Instructions:
  • Ensure specimen is frozen before shipping.
  • Ship on dry ice, sample must remain frozen during shipping.
     
See link to Specimen Collection and Processing for Coagulation Specimens.
Test Performed at or Referral Lab UM Special Coag (K)  (UMMC East Bank)


Interpretive

Therapeutic Range:

The therapeutic anti-Xa range for fondaparinux has not been established. In patients treated with 2.5 mg fondaparinux daily the peak steady-state plasma concentration is on average 0.39 to 0.50 mcg/mL approximately 3 hours post-dose and the minimum steady-state plasma concentration is 0.14 to 0.19 mcg/mL. In patients treated with 5 mg (body weight <50 kg), 7.5 mg (body weight 50-100 kg), and 10 mg (body weight >100 kg) fondaparinux once daily, the mean peak steady-state plasma concentration is approximately 1.20 to 1.26 mcg/mL and the mean minimum steady-state plasma concentration is approximately 0.46 to 0.62 mcg/mL.

[Arixtra Prescribing Information version 9/2013. GlaxoSmithKline, Research Triangle Park, NC and Garcia et al. Chest 2012; 141:e24s-e43S]

 

 

Use:Fondaparinux is a synthetic anticoagulant with selective inhibition of activated factor X (factor Xa). Fondaparinux induces a conformational change in antithrombin and increases its affinity for factor Xa. Inhibition of factor Xa leads to decreased thrombin generation and thrombus development. Fondaparinux has a half-life of approximately 17 hours which allows once-daily dosing. It is almost completely excreted by the kidneys. Fondaparinux is approved for the prophylaxis and treatment of venous thromboembolic events. Laboratory monitoring of Fondaparinux is possible by utilizing factor Xa inhibitory activity of the drug. Anti-Xa assay (used for monitoring heparin) is modified by using a standard curve constructed with Fondaparinux.


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