Heparin Anti-Xa

Single-analyte tests

• Heparin Anti-Xa 117101

  Plasma · Fasting not stated · Turnaround 1 - 3 days

  Method and collection

  Method

  The heparin anti-Xa assay is based on the ability of heparin to inhibit the activity of activated factor X (Xa) in the reagent. The reagent includes excess antithrombin, making the heparin in the sample the rate-limiting reagent for Xa inhibition. Heparin in the patient sample inhibits the enzymatic conversion of a Xa-specific chromogenic substrate to colored product by factor Xa. Standard curves are created using multiple concentrations of UFH and LMWH and are used to calculate concentration in the patient plasma.

  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, 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 and carefully remove the plasma using a plastic transfer pipette, being careful not to disturb the cells. Transfer the plasma into a Labcorp PP transpak frozen purple tube with screw cap (Labcorp No. 49482). Freeze immediately and maintain frozen until tested. To avoid delays in turnaround time when requesting multiple tests on frozen samples, please submit separate frozen specimens for each test requested . Please print and use the Volume Guide for Coagulation Testing to ensure proper draw volume.

  Reference notes

  Reference intervals indicate therapeutic levels. 11 Target Ranges for Treatment of Venous Thromboembolism (VTE) Unfractionated Heparin (UFH) <0.30-0.70 IU/mL (UFH sample obtained 6 hours after initiation or dose adjustment) Low Molecular Weight Heparins (LMWH) | (LMWH sample obtained 4 hours following subcutaneous injection) Enoxaparin (Lovenox) 0.60-1.00 IU/mL for twice daily dosing; >1.00 IU/mL for once daily dosing Nadroparin (Fraxiparine) 0.60-1.00 IU/mL for twice daily dosing; 1.30 IU/mL for once daily dosing Tinzaparin (Innohep) | 0.85 IU/mL for once daily dosing Dalteparin (Fragmin) | 1.05 IU/mL for once daily dosing

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