Antithrombin III Activity, Plasma

ATIII - NCMC

1 mL plasma from Blue Top (3.2% Na Citrate)

Full blue top tube or 1.0 mL plasma frozen

• It is imperative that the tube be completely filled to frosted line. The ratio of blood to anticoagulant is critical for valid coagulation results. If obtaining blood with a syringe, fill the light blue-top (sodium citrate) tube first.
• If patient is on heparin, specimen must be centrifuged and separated within 1 hour of draw.
• Heparin contaminated tube is not acceptable.
• Keep specimen anaerobic.
• Patients with an extremely high hematocrit may require special tubes before obtaining blood for coagulation testing. Please contact the lab for further information.

Centrifuge within 1 hours of collection following the double spin process to produce platelet poor plasma.

• Using a plastic transfer pipette, remove plasma and transfer to a properly labeled polypropylene tube
• Re-spin plasma
• Remove plasma using a plastic transfer pipette and transfer to a properly labeled polypropylene tube
• Freeze plastic tube

Specimen Type	Temperature	Time
Whole blood Na Cit  on heparin	Ambient	1 hour
Whole blood Na Cit (unopen/unspun)	Ambient	4 hours
Plasma Na Cit (open/spun)	Ambient	4 hours
Plasma Na Cit double spun and separated	Frozen -20 C	2 weeks

• Clotted
• Serum received instead of Sodium Citrate plasma 
• Specimen past stability 
• Frozen plasma received thawed 
• Underfilled or Overfilled, blood/anticoagulant ratio must be 9/1; Specimens must be between 90% -110% full 
• Collected in a 3.8% Sodium Citrate tube instead of 3.2% Sodium Citrate tube 
• Drawn in outdated/expired tube 
• Hemolyzed, icteric, or lipemic sample  

Monday through Sunday; Continuously

Same day

80-120%

Antithrombin (AT), or Heparin Cofactor I, is the major inhibitor of blood coagulation and is essential for effective heparin therapy. By inhibiting the coagulation proteases, especially thrombin, FXa and FIXa, AT prevents uncontrolled coagulation and thrombosis. Antithrombin deficiency is associated with a high risk of thromboembolic disorders.

The Antithrombin assay can be used to exclude or diagnose hereditary deficiency in patients with a tendency toward thromboembolism, in pre-operative stages, before prescription of oral contraceptives, DIC, nephritic syndromes, liver diseases and in therapy with heparin or antithrombin concentrates.

In addition to congenital AT III deficiency, decreased AT III activity can be seen in association with severe liver disease, nephrotic syndrome, disseminated intravascular coagulation and other disease states where consumption is increased. AT III activity may also be decreased in patients on heparin therapy.