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Specimen Collection Manual and Test Catalog

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HEPARIN, UNFRACTIONATED

Geisinger Epic Procedure Code:  LAB2430    Geisinger Epic ID:  17589

SPECIMEN COLLECTION
Specimen type: 

Platelet-poor plasma


Preferred collection container: 
Alternate collection container: 
Other size blue-top (3.2% sodium citrate) tubes (e.g., 1.8 mL, 4.5 mL)
Specimen required: 

1 mL


Special notes: 
  • If the patient’s hematocrit (HCT) is >55%, the volume of anticoagulant in the tube must be adjusted. Contact a performing location for sodium citrate adjusted tubes or instruction for how to adjust the sodium citrate.
  • When possible, use fresh venipuncture.
  • Avoid prolong tourniquet time (< 1 minute) and hemolysis during collection as this will alter results.
  • If indwelling catheter or butterfly collection device must be used, draw sample from a non-heparinized lumen or flush the line with 5 mL of saline and discard the first 10 mL of blood.
  • Tubes should be >90% filled.
  • Immediately mix gently after collection by inverting the tube end over end 5 to 6 times. Avoid vigorous mixing or additional inversion. Observe for the presence of clots or hemolysis and recollect if observed.


SPECIMEN PROCESSING
Processing instructions: 

Centrifuge as soon as possible (within 60 minutes) at designated speed and time to obtain platelet-poor plasma (< 10,000/uL). Remove plasma and re-spin the plasma for 10 minutes at 3000 rpm and submit platelet free plasma.

For a single NaCit blue top tube collection, create 1 aliquot NaCit and if additional plasma remains, create an additional aliquot NaCit. If multiple tubes collected, create 1 aliquot NaCit for each NaCIt blue top tube collected plus one additional aliquot NaCit. Aliquots should be 1.0-1.9 mL and all plasma-based coagulation tests must be moved to aliquot(s).


Transport temperature: 

Plasma (on or off cells): Room temperature 
Plasma off cells: Frozen on dry ice


Specimen stability: 

Room temperature (whole blood): 1 hour 
Room temperature (plasma off cells): 2 hours 
Frozen (plasma) -20°C: 2 weeks 
Frozen (plasma) -70°C: 6 months


Rejection criteria: 

Clotted, hemolyzed, improperly filled tubes, improper anticoagulant ratio (HCT >55% and citrate not adjusted), refrigerated specimens, or stability exceeded. 

Note: Specimen suspected of thawing in transport, indicated by slant in aliquot or specimen in lid of tube, will have testing performed, and the comment “interpret results with caution as thawing suspected” added to results.



TEST DETAILS
Reference interval: 

< 0.1 IU/mL


Critical values/courtesy alerts: 
Greater than 0.99 IU/mL
Additional information: 

Anticoagulation Impact on Coagulation Tests


CPT code(s):  85520
Note: The billing party has sole responsibility for CPT coding.  Any questions regarding coding should be directed to the payer being billed.
The CPT codes provided by GML are based on AMA guidelines and are for informational purposes only.

Test includes: 

International units


Methodology: 
Chromogenic anti-Xa assay
Synonyms: 

Unfractionated heparin, Anti-Xa, Xa, HEPU


Clinical significance: 

Used to quantitate the level of unfractionated heparin in a patient's plasma.

Therapeutic range: varies based on protocol, see Anticoagulation Management for protocols.

Low antithrombin III levels, hemolysis, icterus or lipemia may falsely lower levels. If three (3) consecutive subtherapeutic unfractionated heparin levels recommend checking antithrombin III level and APTT.  If antithrombin level low consider antithrombin III replacement. If APTT > 120 seconds, rule out interference for hemolysis or bilirubinemia and consider heparin monitoring with APTT

Anticoagulation with anti-Xa inhibitors (e.g. apixaban, rivaroxaban) causes false results. If the patient is on anti-Xa inhibitor prior to heparin therapy use an alternative method to monitor heparin.


Doctoral Director(s): 
Michelle Grant DO
Review Date:  09/03/2026

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