Last Modified: 7/10/2020 9:28:22 AM

Medical Necessity Documentation:  
Client Notes:

Must be in the testing lab within 45 minutes of draw.

If patient is on Unfractionated Heparin the specimen will need to be to the testing laboratory within 45 minutes of collection.

Patient Preparation:  
Specimen Requirements:

2.7 mL Whole Blood in a Full Blue Top Tube - 3.2% Buffered Sodium Citrate

Collection Instructions: Draw Peak 4-6 hrs post dose.

Specimens must be filled appropriately see this example

Correct ratio of Blood to Citrate is critical (9:1). Specimens must be filled within +/- 10% of stated volume.

If a Blue Top Tube is collected utilizing a butterfly, a Blue Discard Tube must be drawn first to remove air from the line. If this is not done, the Blue Top Tube will not be filled properly due to the vacuum in tube and a redraw will be required

   Heparinized Patient specimens must be spun within 1 hour of collection - Follow Platelet Poor Collection

Note: Collection of blood for coagulation testing through intravenous lines that have been previously flushed with heparin should be avoided, if possible. 
If the blood must be drawn through an indwelling catheter, possible heparin contamination and specimen dilution should be considered. 
When obtaining specimsn from indwelling lines that may contain heparin, the line should be flushed with 5mL of saline, and the first 5 mL of blood or 6-times the line volume
(dead space volume of the catheter) be drawn off and discarded before the coagulation tube is filled. For those samples collected from a normal saline lock (capped off venous port) twice the dead space volume of the catheter and extension set should be discarded.

Minimum Volume: 1.8 mL Whole Blood from a Clear Blue Top Tube
Neonatal Volume: Not Established
Transport & Storage: Temperature/Stability:

4 hours Ambient
Frozen follow Platelet Poor Collection Rules above.

Rejection Criteria: Frozen in a Frost Free Freezer; over or under filled tubes; 3.8% Sodium Citrate; clotted; underfilled; overfilled; inappropriate temperature; HCT >55%; cell volume > 1/2 the tube volume; Re-frozen; Thawed specimens
Reference Range: Refer to Interpretive Results
Critical Ranges:  
Test Comments:

Results will flag abnormal <0.30 and >1.0 IU/mL

LMWH Therapeutic Treatment Range 0.5 - 1.0 IU/mL   The above TREATMENT  therapeutic range is not appropriate to evaluate prophylactic LMWH dosing.

LMWH/UFH Anti-Xa test Test is NOT to be used for the determination of the activity of concentration of factor Xa or anticoagulants other than UFH and LMWH (e.g. heparinoids, synthetic pentasaccharides, direct factor Xa inhibitors). 

The performance of this test has not been established in neonate and pediatric patient populations. UFH Therapeutic Treatment Range Anti-Xa: 0.3 - 0.7 IU/mL. 

Unfractionated Heparin (Heparin Drips) is monitored by aPTT. The need to order LMWH/UFH Anti-Xa levels for unfractionated heparin will be evaluated on a case by case basis.

Methodology: Chromogenic
Clinical Significance:

Intended use: For the quantitative determination of  Low molecular weight heparin (LMWH) and unfractionated heparin (UFH) activity on plasma from patients undergoing heparin anticoagulant therapy with either UFH or LMWH.

Custom Panel: No


Stat Eligible: Yes
Turn Around Time: 4 hours
Days Performed: Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday
Sites Performed: Parkview Regional Medical Center
PHL Test Code: HEPXA
EPIC Test Code: LAB3090
Alternate Test Names: Factor X; Factor Xa; LMWH ; LMWH/UFH Anti Xa; Low Molecular Weight Heparin; UFH; Unfractionated Heparin
Included Tests:  
CPT Coding: 85520

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