Home PageHome Page


Test Code
SynonymsArixtra; Fondaparinux Anti-Xa assay
Container TypeBlue top tube (buffered sodium citrate) 3.2% sodium citrate is the preferred anticoagulant recommended
Supply Item Numberpicture1072
Specimen TypePlasma
Preferred Volume1 mL (2 mL is recommended if repeat testing is required)
Emergency Minimum Volume1 mL
Specimen ProcessingSeparate plasma from cells and transfer to a standard PAML aliquot tube and freeze.
Store and TransportFrozen - Separate samples must be submitted when multiple tests are ordered.
StabilityRefrigerated 4 hours  Frozen (-20 °C) 6 months  
Unacceptable ConditionHemolysis; clotted specimen; specimen contaminated with heparin (ie, drawn with blood gases)
CPT Codes85520
Interface Order Code85520.Z4
Billing CodeFONDXA.LCA
Reference Ranges
Clinical SignificanceClinical Info: Fondaparinux (Arixtra) is an indirect synthetic factor Xa inhibitor based on the active pentasaccharide site of heparin mucopolysaccharides, and is utilized as an anticoagulant drug for treatment or prevention of thromboembolic events. Its antithrombotic mechanism is antithrombin-mediated selective inhibition of factor Xa after binding fondaparinux with antithrombin. However, fondaparinux does not inactivate thrombin and has no effect in platelet function or fibrinolysis. The Fondaparinux Activity assay allows the determination of the plasma levels of fondaparinux by measuring its acceleration of inhibition of activated factor X using a chromogenic substrate method using calibration curve calculated with a commercial Arixtra (fondaparanux) calibrator. This assay cannot be used to monitor patients receiving unfractionated or low molecular weight heparins. Fondaparinux has a half life of approximately 17-21 hours in healthy normal individuals, however, it can be prolonged in patients with renal impairment because fondaparinux is mainly eliminated in urine. While patients treated with fondaparinux are not typically monitored, there is clinical need for monitoring and therapeutic assessment in patients with bleeding or thrombotic complications. In patients undergoing treatment with fondaparinux sodium injection 2.5 mg, once daily, the peak steady-state plasma concentration is, on average, 0.39 to 0.50 mg/L and is reached approximately 3 hours post-dose. In these patients, the minimum steady-state plasma concentration is 0.14 to 0.19 mg/L. In patients with symptomatic deep vein thrombosis and pulmonary embolism undergoing treatment with fondaparinux sodium injection 5 mg (body weight < 50 kg), 7.5 mg (body weight 50 to 100 kg), and 10 mg (body weight > 100 kg) once daily, the body-weight-adjusted doses provide similar mean steady-state peaks and minimum plasma concentrations across all body weight categories. The mean peak steady-state plasma concentration is in the range of 1.20 to 1.26 mg/L. In these patients, the mean minimum steady-state plasma concentration is in the range of 0.46 to 0.62 mg/L. (Prescribing information for Arixtra from GlaxoSmithKline, Oct 2010.

Interface Codes
typeorder codetest descriptionresult coderesult descriptionunitsdecimal placesloinc code
o85520.Z4Fondaparinux Level
r85520.Z4Fondaparinux Level85520.Z4Fondaparinux Levelmg/L 49060-7