Antithrombin III Antigen

Catalog information reviewed: August 24, 2026 by the Sunridge Medical clinical team.

What this laboratory test evaluates

DetailsAntithrombin III Antigen – Aids in characterization of Antithrombin deficiency (AT, previously referred to as Antithrombin III) which is associated with increased thrombotic risk. Type I deficiency is characterized by reduction in activity and antigen levels simultaneously. With type II deficiency, activity levels are lower in comparison to the antigen levels (dysfunctional protein). Acquired deficiency, more common than inherited defects, can occur due to: liver disease, nephrotic syndrome, heparin therapy, disseminated intravascular coagulation (DIC), sepsis, and L-asparaginase chemotherapy.

Note: Target-specific anticoagulant therapy (anti-Xa medications, direct thrombin inhibitors) may cause false positive results for Lupus anticoagulant testing but do not impact the Cardiolipin, B2GPI and Phosphatidylserine-Prothrombin antibody testing.

What type of sample is required for this test?1 mL frozen platelet-poor plasma collected in 3.2% sodium citrate (light blue-top) tube
Test ResourcesFor more information, please consult your healthcare provider.

Additional test information

Antithrombin III Antigen – Aids in characterization of Antithrombin deficiency (AT, previously referred to as Antithrombin III) which is associated with increased thrombotic risk. Type I deficiency is characterized by reduction in activity and antigen levels simultaneously. With type II deficiency, activity levels are lower in comparison to the antigen levels (dysfunctional protein). Acquired deficiency, more common than inherited defects, can occur due to: liver disease, nephrotic syndrome, heparin therapy, disseminated intravascular coagulation (DIC), sepsis, and L-asparaginase chemotherapy.

Collection and processing

• Sample type: Plasma
• Fasting: No
• Estimated laboratory processing: Results should be available in 2 – 5 business days after the sample is collected

How Sunridge uses laboratory information

Sunridge considers the medical question, symptoms, history, medications, prior results, and whether the finding could change care before recommending testing. A laboratory result is not interpreted in isolation and does not establish a diagnosis by itself.

Before requesting this test

Availability, collection requirements, eligibility, and processing estimates can change. Sunridge reviews each request and, when appropriate, creates the order through Fullscript. Follow the current instructions supplied with the approved order.