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The University of Chicago Medicine Laboratories

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Specimen Collection and Handling

Transfusion

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Mayo Clinic Laboratories

Test Code HEPA Unfractionated Heparin Assay by Anti - Xa

Specimen and Container/Tube

Specimen Type: Plasma

Preferred Specimen: Light Blue Top Tube, 3.2% Sodium Citrate

Other Acceptable specimens: N/A

Volume

Preferred Volume: 2.0 mL

 

Minimum Volume: 1.0 mL

Specimen Stability

Storage Temperature

Stability

Room temperature

4 hours

Refrigerated

not acceptable

Frozen

30 days

Collection Instructions

Collect specimen per standard laboratory collection procedures. 

 

Once each blue top tube is completely filled, gently invert the sample tube at least five times to ensure complete mixing of the contents.

Specimen Handling and Transport Instructions

UCMC Onsite Instructions: 

Collect specimen per standard collection procedure and send to laboratory immediately. 

 

NOTE: Once each blue top tube is completely filled, gently invert the sample tube at least five times to ensure complete mixing of the contents.

 

UCMC Offsite and UC MedLab Outreach Instructions: 

  • Collect specimen per standard collection procedure.
  • Once each blue top tube is completely filled, gently invert the sample tube at least five times to ensure complete mixing of the contents.
  • Centrifuge specimens at >2500 x g for 10 minutes at room temperature.
  • Carefully remove plasma from cells using a plastic transfer pipette avoiding buffy coat.
  • Aliquot removed plasma into 2 plastic tubes containing a minimum of 1.0 mL of specimen in each tube.
  • Plasma samples must then be frozen at -20oC.
  • Once solidly frozen, they must be shipped on dry ice. Samples that have thawed in transit will be rejected.

Rejection Criteria

  • Common specimen rejected situations include: incorrect specimen type, insufficient volume, missing or incomplete specimen identifiers, incorrect specimen transport, or specimens outside stability limits. 
  • Specimens that have wrong ratio of blood to anticoagulant (fill volume), clotted or grossly hemolyzed.

Reference Values

 

Test

Age

Sex

Reference Range

N/A

N/A

N/A

N/A

Critical Values

Analyte

Unit

Low

High

Age

N/A

N/A

N/A

N/A

N/A

Turnaround Time

Turnaround times are relative to the time the specimen is received in the test laboratory. 

STAT Turnaround Time: N/A

 

Routine Turnaround Time: 4 hours

 

Testing Schedule:  24/7

Clinical Indications

Monitoring of unfractionated heparin in settings where aPTT is unreliable.

Methodology

Chromogenic, anti-Xa

CPT Codes

85520 

LOINC Codes

3274-8

Synonyms/Keyword Search

Anti-Xa; Unfractionated heparin by anti-Xa;

Heparin level; Heparin level by anti-Xa

Additional Information

Unfractionated heparin level is monitored by functional anti-Xa assay.

For monitoring of heparin therapy the frequently employed target range is 0.3-0.7 anti-Xa Units/mL (e.g., for treatment of venous thrombosis).

    

For the lower intensity anticoagulation range of aPTT 50-70 seconds (e.g., as in guidelines from American College of Chest Physicians), the corresponding range is currently <0.10-0.25 anti-Xa Units/mL.

 

Testing for unfractionated heparin level may be added on to an existing order only up to one hour following the time of blood draw due to technical considerations of this assay.

 

3.2% sodium citrate light blue top tubes must have 9 to 1 ratio of blood to anticoagulant

Last Review Date

05/28/2024