Test Overview

Test Methodology

Chromogenic Substrate Assay

Test Usage

Used to monitor treatment with Arixtra (fondaparinux) when clinically indicated. Dosing protocols for DVT prophylaxis and treatment of DVT/PE have been validated by empiric clinical trials. Clinical monitoring with Arixtra levels is not necessary for most patients.

Reference Range*

Normal individuals have no Arixtra activity.
Expected Therapeutic Ranges:
DVT prophylaxis (Arixtra 2.5mg qd)
3 hours after dose: 0.39-0.50mg/L
Trough: 0.14-0.19 mg/L drawn just prior to next dose.
Treatment of thrombosis (Arixtra 5-10mg qd)
3 hours after dose: 1.20-1.26 mg/L
Trough: 0.46-0.62 mg/L drawn just prior to next dose.

* Reference ranges may change over time. Please refer to the original patient report when evaluating results.

Test Details

Days Test Performed

Daily, 24 hours

Analytic Time

2 hours

Soft Order Code


MiChart Code

FONDAPARINUX (Arixtra), Anti-Xa



Factor Xa Inhibition
Anti-Xa Arixtra
Chromogenic Xa
Xa Chromogenic
Anti-Xa Fondaparinux
Coagulation Factor Xa Inhibition
Arixtra Anti-Xa
Factor 10a Inhibition
Anti-10a Arixtra

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STAT Availability

STAT requests for this test will be performed on a STAT basis (supervisory staff approval is not required).

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Specimen Requirements

Offsite Collection Instructions

The sample should be drawn 3 hours after injection of drug in order to compare to published peak levels. Collect specimen in a blue top (citrate 3.2%) tube. Mix by inversion. Specimen should arrive at lab within 3 hours of collection; transport at room temperature. Alternatively, centrifuge, aliquot plasma into a plastic vial, and freeze the specimen within 4 hours of collection. Transport frozen specimen on dry ice. Collection of the blood through lines that have been previously flushed with heparin should be avoided. If the blood must be drawn through a VAD (vascular access device), the line should be flushed with 5 mL of saline and the first 5 mL of blood or six dead space volumes of the VAD discarded.

Rejection Criteria

Specimens will be rejected if not properly filled, clotted, grossly hemolyzed, contaminated with heparin, or received outside acceptable time limits.


Test is not indicated if the patient is receiving unfractionated heparin or other Anti-Xa drugs.


Blue Top Tube

Normal Volume

Full 2.7mL tube or 1mL plasma aliquot

Minimum Volume

Full 1.8mL tube or 1mL plasma aliquot

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