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Direct Chromogenic Anti-Xa Factor Assay (Factor Xa Activity)

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

This test measures the activity of Factor Xa, an enzyme involved in blood clotting, using a chromogenic method. It helps assess anticoagulant effectiveness, especially in patients on direct oral anticoagulants (DOACs).

Quick summary

["This test evaluates how well your blood is being managed to prevent clots when taking certain blood thinners."]

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

Key facts at a glance

LOINC
111945-2
Short code
Dx chrctr Stom Endscpy
Synonyms
Dx chrctr Stom Endscpy
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
endoscopy
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

The test detects the presence and level of Factor Xa, an activated clotting protein. Chromogenic assays use a color-producing substrate to quantify its activity. This method is precise for monitoring specific anticoagulant therapies.

Why It’s Ordered

Your healthcare provider may order this test if you’re on direct oral anticoagulants (like dabigatran, apixaban, or rivaroxaban) to ensure your medication is working as intended. It’s also used in cases of suspected bleeding or clotting disorders related to these drugs.

Sample Collection and Preparation

A blood sample is drawn from a vein, typically in the arm. The test measures Factor Xa activity in plasma, which is separated from blood cells immediately after collection to avoid interference.

What It Means for Your Health

Elevated Factor Xa activity may indicate insufficient anticoagulation, increasing risk of clots. Low or normal levels suggest effective blood thinning. Results help guide dose adjustments to balance clot prevention and bleeding risks.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Direct Anti-Xa Factor Test

Frequently asked questions

How often will I need this test?
The frequency depends on your treatment plan. Your doctor may order it weekly, biweekly, or monthly, especially if you’re on a new DOAC or have complex medical conditions. Follow your provider’s instructions closely.
What are the possible side effects of this test?
Blood tests like this are generally safe, but you may experience mild bruising, swelling, or discomfort at the injection site. Rarely, bleeding at the site can occur. Inform your doctor if you notice unusual bleeding or signs of infection.
Can I eat or drink before this test?
You can eat and drink normally before this test unless instructed otherwise. Avoid alcohol for 24 hours before testing, as it may affect blood clotting measurements.
  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