Low molecular weight heparins (LMWH) (dalteparin, enoxaparin and tinzaparin) are usually preferred over unfractionated heparin in the prevention of venous thromboembolism because they are as effective and they have a lower risk of heparin-induced thrombocytopenia. The standard prophylactic regimen does not require anticoagulant monitoring. Routine monitoring of anti-Xa activity is not usually required during treatment with low molecular weight herparins but may be necessary in patients at increased risk of bleeding(e.g. in renal impairment and those who are underweight or overweight).
The therapeutic range for LMWH anti-Xa activity is generally 0.6 to 1.0IU/mL. Pre-dose levels are performed to assess heparin accumulation (0.2 to 0.4IU/mL), however this is for once daily dosing regimens and can differ among individual patients dependent on clinical circumstances. Clinicians should seek the advice of the on-call Haematologist if they are unsure on how to interpret the anti-XA activity results.
The volume of blood in coagulation samples must lie within the volume range as indicated by the size of the black fill arrow present on tubes. Volumes above or below the arrow will result in sample rejection to ensure validity of results.
Age of Sample
Samples will be rejected if received more than 2 hours post venepuncture.
- 2 blue top (sodium citrate) samples
- All coagulation tubes must be adequately filled (see above)
- All coagulation tubes must be mixed several times by gentle inversion immediately after venepuncture. Mixing the sample with the anticoagulant stops the sample clotting within the tube.
- It is not possible to provide results on clotted, insufficient, lipaeamic, or haemolysed samples. These will be rejected with the appropriate comment.
- Samples tubes that have expired cannot be accepted.