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| Test Description |
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Test Name
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Antithrombin Activity (Functional) |
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Synonym(s)
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AT III Activity |
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Description
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Antithrombin (AT) inactivates the serine proteases of the coagulation cascade (IIa, Xa, XIa, IXa) by binding to the active site and forming a complex. This function is accelerated by glycosaminoglycans including heparin. Hereditary heterozygous AT deficiency is associated with recurrent thrombosis, mostly venous. It is inherited in an autosomal dominant fashion. Acquired AT deficiencies may be seen in liver disease, post operative state, nephrotic syndrome, DIC, extensive thrombosis and women using oral contraceptives. |
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Methodology
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Clotting |
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Performed
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Monday – Friday
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Turnaround Time
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1-3 days |
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Specimen Requirements
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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:
- 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.
- 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.
- 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)
- Double-centrifugation is critical for accurate results as platelet contamination may cause erroneous results.
- Plasma must be frozen within 4 hours of collection.
- CRITICAL WARNING: Specimen must remain frozen until testing. Submit separate aliquots when multiple tests are ordered on same patient specimen.
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Rejection Criteria
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Plasma hemolyzed, thawed or contaminated with heparin. |
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CPT Code(s)
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85300 |
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Reference Range
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84 – 124%
Intrepretation Note: Functional antithrombin values may decrease with oral anticoagulants. Patient should be off oral anticoagulants for 2 weeks for accurate measurement. Functional antithrombin values may be increased in patients on heparin therapy. Patients who are actively thrombosing may have low functional antithrombin values.
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Contact Information
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Hemostasis Lab: 214-645-5067
Customer Service: 214-645-7057, Toll Free 877-887-8136 |
Last Modified: 01/05/2011 |
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