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Factor Xa Activity (Antithrombin-Coated Assay)

Published: August 9, 2026Updated: August 16, 2026

This test measures how well Factor Xa, an enzyme involved in blood clotting, is inhibited by natural blood proteins. It helps assess your risk of blood clots or bleeding disorders.

Quick summary

["Understanding your Factor Xa activity can guide treatment for bleeding or clotting risks."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
80603-4
Short code
Fact XI Inhib PPP Ql
Synonyms
Fact XI Inhib PPP Ql
Category
chemistry
Sample
plasma
Container
Lavender-top (EDTA) or Green-top (Heparin)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
coag
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

What This Test Measures

Factor Xa is a key enzyme in the blood clotting process. When blood clots form, Factor Xa converts fibrinogen into fibrin, which helps stabilize clots. This test evaluates how effectively natural anticoagulants (like antithrombin) inhibit Factor Xa activity in your blood.

Why It’s Ordered

Your healthcare provider may order this test if you have a history of bleeding disorders, clotting issues, or are taking anticoagulant medications. It can also be used to monitor treatment effectiveness in conditions like thrombophilia or during pregnancy-related clotting risks.

Sample Collection and Preparation

Blood is drawn from a vein, typically in the arm. The sample is collected in a tube that prevents clotting and is sent to the lab for analysis. This test is usually performed on plasma, the liquid part of blood after clotting factors are removed.

Test Method and Process

The test uses a specialized immunoassay method to detect and quantify Factor Xa activity. A chemical reaction is triggered that produces a measurable signal, indicating how well Factor Xa is inhibited by natural anticoagulants in your blood.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Factor Xa Activity

Frequently asked questions

How does Factor Xa activity relate to my health?
Low Factor Xa activity may suggest an inherited or acquired deficiency in antithrombin or other anticoagulants, increasing your risk of bleeding. High activity could indicate a clotting disorder or inadequate anticoagulant therapy. Your provider will interpret results in the context of your medical history and symptoms.
What do my results mean for my treatment?
If you’re on anticoagulant therapy (e.g., for clotting prevention), abnormal Factor Xa activity may help adjust your medication dose. If you have bleeding tendencies, your provider may use these results to guide treatment decisions, such as supplements or blood transfusions.
Can this test help diagnose specific conditions?
Yes, this test can help diagnose conditions like antithrombin deficiency, which is linked to an increased risk of blood clots. It may also be used in research or specialized clinical settings to evaluate coagulation pathways in complex cases.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy