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UW Health SMPH
American Family Children's Hospital

UW Hospital and Clinics Lab Test Directory

Test Name: Antithrombin III, Activity

Test Code(s): A3AC / XAT3

CPT Code(s): 85300

Methodology: Chromogenic Anti-Xa Assay

Clinical Significance: Antithrombin is a protein that inhibits thrombin, activated factor X (Xa) and other serine protease enzymes. This test is usually part of a hypercoagulation workup. Test may be falsely low when patient is on heparin.

Days Performed: Mon-Fri, dayshift - day varies. Specimens are accepted at any time. Testing required during off hours must be approved by a Coagulation physician. Call 263-5005 before collection.

Turnaround Time: Stat: 1 working day.
Routine: 4 - 7 days.

Specimen Requirements

Specimen: Blood

Collection Instructions: Do NOT draw through a line containing heparin. The venipuncture MUST be atraumatic to avoid hemolysis and contamination with tissue factors and platelets. Tube must be allowed to fill completely.  Indicate if patient is receiving anticoagulant (warfarin/Heparin/Vitamin K antagonist), direct thrombin inhibitor or fibrinolytic agent therapy and duration.

If unable to collect 1.8 ml tube (pediatrics only) please call Core Coagulation Lab at 263-9617 or Special Coagulation Lab at 263-5005 for alternate tube and instructions.  

Collection Container: Preferred: Light blue top (3.2% NaCitrate)

Collection Volume: Preferred: Full 3.5 mL tube
Pediatrics: Pediatric tube filled to fill mark

Sample Analyzed: Plasma

Volume Required: Preferred: 1 mL
Pediatrics: 0.5 mL

Specimen Processing: Centrifuge specimen to yield platelet poor plasma (platelet count should be less than 10 K/L). Separate plasma and transfer to plastic tube or vial.  Freeze plasma within 4 hours of collection at -20C or below.  

Specimen Transport: Transport whole blood specimen at room temperature to UWHC Core Laboratory (B4/220) within 4 hours of collection. See Specimen Processing for instructions if transport criteria are not met.  Transport frozen plasma aliquot on dry ice to UWHC Core Laboratory (B4/220).

Outreach Specimen Transport: Centrifuge specimen to yield platelet poor plasma (platelet count should be 10 K/µL or less). Separate plasma and transfer to labeled plastic tube and spin again. Transfer plasma from second spin to clean plastic labeled tube or vial. Indicate on tube "spun twice". Freeze plasma within 4 hours of collection at -20°C or below.

Unacceptable Criteria: Hemolyzed specimens, clotted specimens, partially filled tubes and whole blood specimens greater than 4 hours old when received by the laboratory are not acceptable.

Stability: Ambient: 4 hours on a spun tube
Refrigerated: Not acceptable
Frozen: 2 weeks at -20C; 6 months at -70C


Reference Interval:
 0 days-2 months:  40-110%
 3-5 months:  70-120%
 6 months and up:  85-135%

AT3 Antithrombin  ATIII

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