Anti-Xa assay
Synonyms
Xa assay, Low Molecular weight heparin assay
Clinical Indications
Monitoring of prophylactic and therapeutic doses of LMWH is not
required routinely. However, anti-Xa assay may be of use in
individuals for whom the standard weight adjusted dose may be
unreliable. These include patients with renal failure, the obese,
the pregnant, neonates and infants, those with unexpected bleeding
on LMWH.
Samples for peak levels of anti-Xa activity should be taken 4-6
hours after subcutaneous administration. For trough levels the
sample taken 24 hours after administration may be
informative.
Note: this is NOT the same as a Factor X
assay
Request Form
Request via ICE
Availability
Monday-Friday 9am-5pm (Tests recieved outside this time will be
frozen for processing on the next routine day)
Specific Criteria
Patient should be bled with minimal stasis
Patient Preparation
Patient should ideally be at rest
Turnaround Time
Same day.
Specimen
Fresh citrated Blood (sample MUST reach the laboratory within 1
hour of collection)
Volume
4.5 ml
Container
Blue capped vacutainer tube
Collection
Clean venepuncture; sample transported to laboratory immediately
after collection
Causes for Rejection
Underfilled, clotted or haemolysed samples
Reference Range
Therapeutic level: 0.35 - 0.7 anti-Xa units/mL