Factor II Activity, Clotting

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

What this laboratory test evaluates

DetailsFactor II Activity, Clotting – The Factor II Activity clotting assay provides a quantitative level of Factor II (also known as Prothrombin) activity. Factor II/Prothrombin is essential for normal hemostasis and deficiencies are associated with increased bleeding risk. As a vitamin K- dependent clotting factor, decreased levels are observed with vitamin K antagonists (eg. warfarin therapy) and vitamin K deficiency. Deficiencies may also occur with hepatic dysfunction or as a result of inhibitor development. Antibodies to prothrombin can occur in patients with anti- phospholipid antibodies and can cause significant clinical bleeding; however, because these antibodies bind to a nonactive portion of the molecule, increased clearance occurs, so that a deficiency rather than an inhibitor is detected. Congenital Factor II deficiency is extremely rare.

Anticoagulant interference: if not clinically contraindicated, avoid warfarin therapy for approximately 2 weeks before testing. Direct Xa or thrombin inhibitor therapy may cause falsely low levels (avoid for approximately 2-3 days before testing if not clinically contraindicated.

The Factor II Activity, Clotting assay IS NOT intended to identify the Prothrombin 20210G>A Gene Mutation, which is associated with the increased thrombotic risk.

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

Factor II Activity, Clotting – The Factor II Activity clotting assay provides a quantitative level of Factor II (also known as Prothrombin) activity. Factor II/Prothrombin is essential for normal hemostasis and deficiencies are associated with increased bleeding risk. As a vitamin K- dependent clotting factor, decreased levels are observed with vitamin K antagonists (eg. warfarin therapy) and vitamin K deficiency. Deficiencies may also occur with hepatic dysfunction or as a result of inhibitor development. Antibodies to prothrombin can occur in patients with anti- phospholipid antibodies and can cause significant clinical bleeding; however, because these antibodies bind to a nonactive portion of the molecule, increased clearance occurs, so that a deficiency rather than an inhibitor is detected. Congenital Factor II deficiency is extremely rare.

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.