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Blood Sciences

Blood Test Information

Anti Xa
(a.k.a Heparin -low molecular weight, Factor Xa, LMW, LMWH)
minimum sample volume required ~ 2.7ml

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Tube type: 9NC

Special instructions
For assessment of peak anti-Xa activity, a citrate sample should be taken 4 hours after subcutaneous administration.

If heparin accumulation is suspected, a trough sample at 12 hours may be useful.

Warning: Blood samples taken through in situ lines cannot be accepted as they are commonly contaminated with unfractionated heparin.

Haemolysed samples should not be tested. Time limit for add on = 8 hours

Recommend advice from clinical haematologist before requesting assay. Please inform the haematology laboratory prior to sending sample.

Urgent samples will be analysed within one hour from receipt of sample, laboratory must be informed prior to receiving sample.

Contact Laboratory before requesting

Reference range
Once daily regime therapeutic range: 0.8-1.6 Twice daily regimes therapeutic range: 0.5-1.1


Turnaround Time
1 day

Department: Haematology

Clinical Application
Please note: routine monitoring of anti-Xa activity is not recommended in clinically stable adults with uncomplicated disease. Monitoring may be warranted for patients with renal insufficiency, extremes of body weight, during pregnancy or in paediatrics.


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