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UW Health SMPH
American Family Children's Hospital

UW Hospital and Clinics Lab Test Directory

Test Name: Fondaparinux Level by anti-Xa

Test Code(s): FONDA / HCFONDA

CPT Code(s): 85520

Methodology: Chromogenic Anti-Xa Assay

Clinical Significance: The plasma level of Fondaparinux is determined by the measurement of anti-Xa activity.

Days Performed: Daily- Specimens are accepted at any time. Testing required during off hours must be approved by a Coagulation physician. Call (608)263-5005 before collection.

Turnaround Time: Stat: 2 hours.
Routine: 1 day.

Specimen Requirements

Specimen: Blood

Collection Instructions: Do NOT draw through a line containing heparin as this method is unable to distinguish fondaparinux from heparin in the sample.  The venipuncture MUST be atraumatic to avoid hemolysis and contamination with tissue factors and platelets.

Collection Container: Preferred: Light blue top (3.2% NaCitrate)

Collection Volume: Preferred: Full 3.5 mL tube
Pediatrics: Pediatric tube filled to fill mark

Sample Analyzed: Plasma

Volume Required: Preferred: 1 mL
Pediatrics: 0.3 mL

Specimen Processing: Centrifuge specimen to yield platelet poor plasma(platelet count of plasma should be less than 10K/L). Separate plasma and transfer to plastic tube or vial. Freeze plasma at -20C or below.

Specimen Transport: Transport whole blood specimens at room temperature to UWHC Core Laboratory(B4/220) within 1 hour of collection. See Specimen Processing for instructions if transport criteria are not able to be met.  Transport frozen plasma aliquot on dry ice to UWHC Core Laboratory(B4/220).

Unacceptable Criteria: Hemolyzed specimens, clotted specimens, partially filled tubes and whole blood specimens greater than 1 hour old when recieved by the laboratory are not acceptable.

Stability: Ambient: 1 hour off cells
Refrigerated: Not acceptable
Frozen: 2 weeks at -20C; 6 months at -70C


Interpretive Guidelines:

Therapeutic range is 0.60-1.50 mg/L for fondaparinux when collected 3 hours post dosing.  Estimated prophylactic range is 0.10-0.50 mg/L.


Referenced from Depasse et. al.  "Assessment of three chromagenic and one clotting assays for the measurement of synthetic pentasaccharide fondaparinux (ArixtraTM) anti-Xa activity," Journal of Thrombosis and Haemostasis, 2004, volume 2, 346-379.


The performance characteristics of this test were validated by the UWHC Clinical Laboratories.  The U.S. Food and Drug Administration(FDA) has not approved or cleared this test; however, FDA approval or clearance is currently not required for clinical use of this test.  The results are not intended to be used as the sole means for clinical diagnosis or patient management decisions.  The UWHC Clinical Laboratories is authorized under Clinical Laboratory Improvement Amendments(CLIA) and by all states to perform high-complexity testing.



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