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Specimen Collection Manual and Test Catalog

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ANTITHROMBIN III ACTIVITY

Geisinger Epic Procedure Code:  LAB1770    Geisinger Epic ID:  17587

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 prolonged 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 frist 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 and recollect if observed.


SPECIMEN PROCESSING
Processing instructions: 

Centrifuge specimen immediately at designated time and speed to obtain platelet-poor plasma (<10,000/µL). Using a plastic pipette, carefully remove plasma from cells, avoiding platelet/buffy layer by leaving a thin layer of plasma on top the cells. The centrifuged plasma should be aliquoted (1 mL per aliquot) into clearly labeled polypropylene tubes. The number of tests ordered will determine the aliquots needed. Check the residual specimen for clot and if present discard sample and redraw specimen. If plasma is icteric, lipemic or hemolyzed a lab comment should be generated to notify staff. Freeze upright in non-thaw freezer.


Transport temperature: 

Frozen.


Specimen stability: 

Room temperature (plasma off cells): 8 hours 
Frozen (plasma) -20°C: 30 days 
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: 

80-120%


Additional information: 

Anticoagulation Impact on Coagulation Tests


CPT code(s):  85300
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: 

Antithrombin level


Methodology: 
Chromogenic
Synonyms: 

AT3, Antithrombin 3, Antithrombin


Clinical significance: 

Antithrombin 3 (AT3) is a blood protein produced in the liver that naturally prevents clot formation. AT3 works with heparin to stop clot production mainly by inhibiting thrombin (factor IIa) and factor Xa. Low AT3 levels increase risk of blood clots in patients and decrease response to heparin therapy. AT3 levels are low during or immediately after a blood clot, in patients with kidney or liver disease, and during heparin therapy. If AT3 < 30% and the patient is on heparin therapy consider supplementation with AT3 concentrate if clinically indicated.


Doctoral Director(s): 
Michelle Grant DO
Review Date:  03/04/2025

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