Antithrombin Antigen

Single-analyte tests

• Antithrombin (AT) Antigen (Immunologic) 015057

  Plasma · Fasting not stated · Turnaround 2 - 3 days

  Method and collection

  Method

  Automated (LIATEST) enzyme immunoassay (EIA)

  Preparation

  Do not draw from an arm with a heparin lock or heparinized catheter.

  Collection

  Blood should be collected in a blue-top tube containing 3.2% buffered sodium citrate.1 Evacuated collection tubes must be filled to completion to ensure a proper blood-to-anticoagulant ratio.2,3 The sample should be mixed immediately by gentle inversion at least six times to ensure adequate mixing of the anticoagulant with the blood. A discard tube is not required prior to collection of coagulation samples unless the sample is collected using a winged (butterfly) collection system. With a winged blood collection set a discard tube should be drawn first to account for the dead space of the tubing and prevent under-filling of the evacuated tube.4,5 When noncitrate tubes are collected for other tests, collect sterile and nonadditive (red-top) tubes prior to citrate (blue-top) tubes. Any tube containing an alternative anticoagulant should be collected after the blue-top tube. Gel-barrier tubes and serum tubes with clot initiators should also be collected after the citrate tubes. Please print and use the Volume Guide for Coagulation Testing to ensure proper draw volume.

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Panels that include this biomarker

• Antithrombin (AT) Deficiency Profile 015594

  2 analytes · Plasma · Fasting not stated · Turnaround 2 - 3 days

  Method and collection

  Method

  AT antigen: Automated (LIATEST) enzyme immunoassay (EIA) AT activity: The patient plasma is mixed with heparin and thrombin. The extent of thrombin inhibition is proportional to the AT concentration of the patient sample. Residual thrombin activity is measured as the rate of conversion of a chromogenic substrate and is used to calculate AT concentration.

  Preparation

  Do not draw from an arm with a heparin lock or heparinized catheter. Ideally, patients should not be on unfractionated heparin or direct Xa inhibitor therapy.

  Collection

  Citrated plasma samples should be collected by double centrifugation. Blood should be collected in a blue-top tube containing 3.2% buffered sodium citrate.1 Evacuated collection tubes must be filled to completion to ensure a proper blood to anticoagulant ratio.2,3 The sample should be mixed immediately by gentle inversion at least six times to ensure adequate mixing of the anticoagulant with the blood. A discard tube is not required prior to collection of coagulation samples, except when using a winged blood collection device (ie, "butterfly"), in which case a discard tube should be used.4,5 When noncitrate tubes are collected for other tests, collect sterile and nonadditive (red-top) tubes prior to citrate (blue-top) tubes. Any tube containing an alternate anticoagulant should be collected after the blue-top tube. Gel-barrier tubes and serum tubes with clot initiators should also be collected after the citrate tubes. Centrifuge for 10 minutes and carefully remove 2/3 of the plasma using a plastic transfer pipette, being careful not to disturb the cells. Deliver to a plastic transport tube, cap, and recentrifuge for 10 minutes. Use a second plastic pipette to remove the plasma, staying clear of the platelets at the bottom of the tube. Transfer the plasma into a Labcorp PP transpak frozen purple tube with screw cap (Labcorp No. 49482). Freeze immediately and maintain frozen until tested. Please print and use the Volume Guide for Coagulation Testing to ensure proper draw volume.

  Reference notes

  In newborns, AT levels are lower than in adults (39% to 89%). Levels gradually reach adult ranges by six months of age.6

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