coagulation factor X inhibitor in plasma; anti-factor Xa heparin assay

Indications

• evaluation for coagulation factor inhibitor, generally factor X autoantibody
• heparin therapy in patients:
  • with lupus anticoagulant
  • also taking warfarin
  • refractory to heparin (> 40,000 units/day)
  • receiving thrombolytic therapy

Reference interval

• < 0.1 anti-Xa heparin units/mL
• therapeutic unfractionated heparin:
  • 0.3 - 0.7 anti-Xa units/mL
• prophylactic unfractionated heparin:
  • 0.2-0.4 anti-Xa units/mL
• LMW heparin:
  • 0.5 - 1.0 anti-Xa units/mL (4 hours post dose, BID dosing)
  • 1.0 - 2.0 anti-Xa units/mL (4 hours post dose, QD dosing)
  • 0.2 - 0.4 anti-Xa units/mL plasma (4 hours post dose, prophylaxis)

Methods

• test does NOT depend upon phospholipid

Specimen

• citrated plasma

More general terms

• clinical coagulation test

Additional terms

• coagulation factor X autoantibody
• coagulation factor X; Stuart factor; Stuart-Prower factor; contains: factor X light chain; factor X heavy chain; activated factor Xa heavy chain (F10)