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Test Code BLOD0668 Heparin/Enoxaparin Anti-Xa, Low Molecular Weight Heparin (LMWH)

Important Note

This test is used to monitor Low Molecular Weight Heparin (e.g. Lovenox) therapy.  This test should not be ordered in place of an activated partial thromboplastin time (APTT).

Useful For

Monitoring Low Molecular Weight Heparin (e.g. Lovenox) therapy


Chromogenic Substrate Assay

Performing Laboratory

Bozeman Health Laboratory Services

Specimen Requirements

Specimen must arrive and be tested within 4 hours of draw.

Specimen Type: Whole blood
Container/Tube: Blue top (3.2% sodium citrate)

Specimen Volume: Full tube

Collection Instructions: Click here to link to a You Tube video tutorial

1. Immediately after draw, invert tubes several times to mix blood with additive.

2. Send specimen in original tube.

3. If there is a delay in transport of >4 hours, specimen must be double-centrifuged to prepare a platelet-free plasma specimen as follows:

a. Immediately centrifuge at 3,200 rpm for 15 minutes.

b. Carefully remove plasma from cells avoiding platelet/buffy coat, and transfer plasma into a plastic tube.

c. Centrifuge plastic tube at 3,200 rpm for 15 minutes.

d. Carefully remove top portion of plasma and transfer plasma into a plastic tube leaving approximately 250 mcL in bottom to discard.

e. Double-centrifuged plasma should be aliquoted (0.5 mL-1 mL each) into clearly labeled plastic tubes. (Glass vial is not acceptable.)

Note: Number of tests ordered will determine number of aliquots needed, generally 1 aliquot per test.

f. Specimens should be frozen at <-40° C, if possible, and sent together in same container with at least 5 lbs of dry ice. Specimens must arrive in a frozen state.

Additional Information: Double-centrifuged specimen is critical for accurate results as platelet contamination may cause spurious results.

Specimen Transport Temperature

Whole blood-Ambient

Specimen Stability


Specmen Type Temperature Time
Whole Blood (unspun) Ambient 4 hours
Plasma Na Citrate (double spun) Frozen 14 days


Reference Values

0.00-0.10 IU/mL


For patients on LMW Heparin:

Therapeutic range: 0.60-1.00 IU/mL 

Prophylactic range: 0.10-0.50 IU/mL


Day(s) Test Set Up

Monday through Sunday

Test Classification and CPT Coding