Anti-Xa assay
Anti-factor Xa (10a) assay indirectly measures the activity of heparin
Most commonly used method is the chromogenic assay
(a chromophore-linked substrate of factor Xa is used)
Used to monitor anticoagulant therapy (esp LMWH), esp in:
- Extremes of weight
- Pregnancy
- Critically ill
- Renal impairment
Use of this assay is usually NOT indicated
NB:
- LMWH = Low-molecular weight heparin
- UH = Unfractionated heparin
Therapeutic ranges of heparin
LMWH: 0.5 to 1.2 IU/mL
UH: 0.3 to 0.7 IU/mL
Prophylactic ranges of heparin
LMWH: 0.2 to 0.5 IU/mL
UH: 0.1 to 0.4 IU/mL
Limitation
- Not usually available
- No Australian consensus guideline
Reference: http://emedicine.medscape.com/article/2085000-overview http://www.australianprescriber.com/magazine/36/3/98/101