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Anti-Xa Factor Activity in Heparin Plasma (24-Hour Monitoring)

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

This test measures how well your blood clots in response to a specific type of blood thinner called heparin, taken over a 24-hour period.

Quick summary

["Helps monitor heparin dose to prevent dangerous blood clots or bleeding risks."]

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

Key facts at a glance

LOINC
45274-8
Short code
LMW heparin ind plt Ab Ser Ql
Synonyms
LMW heparin ind plt Ab Ser Ql
Category
hematology
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
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

Why This Test Matters for Your Treatment

Heparin is a blood thinner used to prevent clots in people with conditions like deep vein thrombosis (DVT), atrial fibrillation, or after certain surgeries. This test checks how effectively heparin works by measuring its ability to inhibit a protein called Factor Xa, which is involved in clot formation. Proper dosing helps balance the risk of clots versus bleeding.

How the Test Works

A blood sample is drawn and tested for heparin’s effect on Factor Xa activity. The test measures how much Factor Xa is blocked over time, typically reported as an anti-Xa level. Results help doctors adjust your heparin dose if needed.

What to Expect Before the Test

You may receive instructions to avoid certain medications (like NSAIDs) or activities (like smoking) that could affect blood clotting. A nurse will draw blood from a vein in your arm, and you may feel a brief pinch or slight discomfort.

Common Results and Next Steps

Results are compared to a target range set by your doctor based on your condition. If levels are too low, your heparin dose may need to be increased. If levels are too high, your doctor may adjust the dose or temporarily stop heparin.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance: Balancing Blood Thinning Risks

Short name

Heparin Anti-Xa Level (24h)

Frequently asked questions

How often should I get this test?
Your doctor will determine the frequency based on your treatment plan. Typically, tests are done 4–6 hours after a heparin dose (for short-term use) or every 24 hours (for long-term monitoring). Follow your healthcare provider’s schedule.
What if my results are outside the target range?
If your anti-Xa level is too low, you may experience clots, while too-high levels could increase bleeding risk. Your doctor will adjust your heparin dose or switch to another blood thinner if needed. Never change your medication without consulting them.
Can I eat or drink before this test?
You can eat and drink normally unless your doctor specifies otherwise. Avoid alcohol or smoking before the test, as they may affect blood clotting.
  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