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HelpTest Code LAB5416 Anti Factor Xa Activity
Performing Laboratory
St. Louis Children's Hospital - Coagulation
Specimen Requirements
Patient Preparation: None
Container/Tube
Preferred: Light blue-top (Citrate) tube (1.8 or 2.7 mL)
Acceptable: Blue-cap (9Cl/1.3) microtainer tube. Call lab at 314-454-4268 if microtainer tube required
Collection Volume: Tube should be full
(Full is to marking on tube label. MINIMUM tube volume for collection is to marking on tube label but may go above line)
Submission Container/Tube: If specimen is coming from outside facility and do not have a STAT spin centrifuge to process, centrifuge and transfer all plasma into a plastic vial, then centrifuge plasma again to get platelet-poor plasma. Aliquot plasma into plastic vial leaving 0.25 mL in the bottom of centrifuged vial. Send to lab STAT
Special Instructions:
|
1. |
Draw a discard tube prior to light-blue top tube. |
|
2. |
Tube(s) should remain stoppered. |
|
3. |
Immediately invert tube/microtainer® gently 8-10 times after collection to ensure proper mixing of blood and anticoagulant (this will avoid specimen clotting). Forward promptly at ambient temperature only. |
|
4. |
DO NOT underfill tube(s) |
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5. |
SPECIMEN MAY NOT BE COLLECTED BY CAPILLARY METHOD |
|
6. |
If the patient has a known hematocrit >55%, contact the lab at 454-4268 for collection instructions and a specially adjusted collection tube(s). |
Sample Rejection
Vacutainer®(s) that are under-filled.
Clotted specimens.
Grossly hemolyzed specimens.
Mislabeled or unlabeled specimens.
Logistics
Test Availability: Monday-Sunday
Cut-off time: None; performed as received
Turnaround Time: Same day; 1 hours from receipt in performing lab
Reference Values
Reference Interval:
| Enoxapin therapeutic range (peak) | |
| VTE treatment, Q12hr dosing: | 0.60-1.00 IUnits/mL |
| VTE treatment, Q24hr dosing: | 1.00-2.00 IUnits/mL |
| Q24hr dosing for renal impairment (CrCl<30 mL/min): | 0.60-1.00 IUnits/mL |
| VTE prevention: | 0.10-0.40 IUnits/mL |
| Anti-Xa therapeutic ranges apply to blood samples drawn 4 hours after last dose (peak) | |
| Unfractionated heparin (UFH) therapeutic range: 0.30-0.70 IUnits/mL | |
| Direct factor Xa inhibitors (rivaroxaban, apixaban): Results must be interpreted qualitatively. No activity detected suggests little anticoagulant activity. | |
| In severe antithrombin deficiency, anti-Xa measurement may be inaccurate. | |
Interpretive guidelines developed in adult populations.
Interpretive guidelines for pediatric patients have not been rigorously defined.
Critical Value: None established
Methodology
Chromogenic
Limitations
- Direct oral anticoagulants which inhibit Factor Xa (rivaroxaban, apixaban, edoxaban) positively interfere with this test (e.g. anti-Xa DOACs prescribed concurrently with LMWH or UFH can produce a falsely elevated LMWH/UFH activities)
Additional Information
FOR SLCH CORE LABORATORY USE ONLY
Lab Processing instructions: GIve specimen to coagulation bench to be spun in STAT Spin centrifuge for 3 minutes @ 8500 rpm. Specimen should be processed with 1 hour after sample collection and aliquoted off cells if testing will not be performed within 1 hour.
Processed Volume: Blood level should be to line on label (may be over)
Analyte Stability:
| Specimen Type | Temperature | Time |
|---|---|---|
| Whole Blood (unprocessed) | Ambient | 1 hours |
| Plasma (processed) | Refrigerated (preferred) | 4 hours or 6 hours off cells |
| Ambient | 4 hours or 6 hours off cells | |
| Frozen (-20c) | 1 month |
Test Classification and CPT Code
85520
LOINC
42679-1
Last Reviewed
06/2025