Factor X is activated both by the extrinsic and intrinsic system before exerting its effect on the conversion of prothrombin to thrombin. Patients who need anticoagulation therapy can be treated with warfarin, which is a vitamin K antagonist. This treatment leads to a decrease in all vitamin K dependent clotting factors and thus a prolonged clotting time of blood. The therapy requires careful monitoring since it is essential to find an optimal balance between risk of thrombosis and management of patients with lupus inhibitors receiving warfarin therapy.

3 mL platelet-poor citrated plasma (light blue 3.2% sodium citrate tube). Freeze plasma within 4 hours of collection in 1 mL aliquots.

Transport frozen.

Minimum volume 2 mL.

Coagulation Drawing Instructions:

1. When drawing coagulation tests, always draw a "pilot" tube (7-10 mL plain red top tube, completely filled). This removes tissue fluid contamination, discard pilot tube.
2. Draw blood in a light blue (3.2% sodium citrate) top tube. Fill tubes as far as vacuum will fill and mix gently. Ratio of anticoagulant and blood must be maintained. Avoid slow flowing draws and traumatic venipunctures.
3. Spin vacutainer – remove plasma avoiding platelet/buffy layer – spin plasma again – remove top portion of plasma and place 1 mL of PLATELET-POOR PLASMA in plastic tube. (Glass tube unacceptable)
4. Double-centrifugation is critical for accurate results as platelet contamination may cause erroneous results.
5. Plasma must be frozen within 4 hours of collection.
6. CRITICAL WARNING: Specimen must remain frozen until testing. Submit separate aliquots when multiple tests are ordered on same patient specimen.