To monitor low molecular weight heparin (LWMH) therapy and sometimes to monitor unfractionated heparin (UFH) therapy
Heparin Anti-Xa
Heparin Anti-Xa
Também conhecido como
Anti-Xa
Xa inhibition
Antifactor Xa heparin
Heparin level
Nome formal
Heparin Anti-Xa
Este artigo foi revisto pela última vez em
Este artigo foi modificado pela última vez em 10 de Julho de 2017.
At a Glance
Why Get Tested?
When To Get Tested?
When you are being treated with LMWH or UFH and your doctor wants to monitor the amount of heparin in your blood
Sample Required?
A blood sample drawn from a vein in your arm
Test Preparation Needed?
None
Accordion Title
Common Questions
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How is it used?Anti-Xa tests are sometimes ordered to monitor and adjust unfractionated heparin (UFH) concentrations in the blood, though the primary monitoring tool for UFH is currently the PTT test. Anti-Xa may be ordered to monitor some patients who have “heparin resistance” – do not respond as expected to UFH – or who have an underlying condition or interfering factor(s) that alter the PTT test result.
Low molecular weight heparin (LMWH) therapy is usually not monitored, but doctors may order anti-Xa tests in some cases. These include patients who are pregnant, obese, very young, elderly and those who have kidney disease or dysfunction. LMWH is primarily cleared from the body by the kidneys. Any condition that decreases kidney function can potentially decrease LMWH clearance, increasing its concentration in the blood and increasing the potential for excessive bleeding.
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When is it ordered?The anti-Xa test is not routinely ordered but may be performed whenever a doctor wants to evaluate UFH or LMWH concentrations in the blood. It may be ordered periodically to monitor UFH therapy, especially when a doctor feels that a patient is not responding as expected to UFH or when the PTT is not useful.
When it is used as a LMWH monitoring tool, anti-Xa is primarily ordered as a “peak” test. It is collected about 4 hours after a LMWH dose is given, when the concentration of LMWH in the blood is expected to be at its highest level. Random and “trough” anti-Xa tests may also be ordered when a doctor suspects that a patient may not be clearing the LMWH at a normal rate. Trough tests are collected just prior to the next dose, when heparin concentrations are expected to be at their lowest.
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What does the test result mean?Anti-Xa results must be evaluated in the context of the type of heparin that a person is receiving (UFH or LMWH and type of LMWH), the timing of the sample collection, and the condition that the person is being treated for. Results from different laboratories may not be interchangeable. Therapeutic reference ranges and the heparins that they are based on vary.
In general, for UFH and LMWH, if concentrations are within an established therapeutic range and the patient is doing well clinically – not clotting, bleeding excessively, or experiencing other complications – then the dosage is considered appropriate. If the anti-Xa concentration is high, then the patient may be getting an excessive dose and/or not be clearing the drug at an expected rate and may be at an increased risk for excessive bleeding.
If the anti-Xa concentration is below the therapeutic range, then the dosage of heparin may need to be increased. When a person is not taking heparin, anti-Xa concentrations should be zero or undetectable.
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Is there anything else I should know?Because of differences in the methods used for measuring anti-Xa and in the test results generated by various laboratories, samples for repeat anti-Xa testing should be sent to the same laboratory.
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How long will I have to take heparin?LMWH and UFH therapy are usually used for short periods of time to help treat and prevent inappropriate clotting. When long-term anticoagulation is required, other drug therapies such as warfarin are usually used. An exception to this is during pregnancy, when heparin is the preferred anticoagulant, but the need for heparin therapy in this case ends at the time of delivery.
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Do I need to tell my other doctors that I am receiving LMWH?Yes, this is information that will be important for doctors and other medical professionals to know when evaluating you for or determining treatment options for other conditions.