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Endogenous Vitamin K Antagonist Activity (Serum/Plasma)

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

This test measures the effect of certain blood-thinning medications on your vitamin K-dependent clotting factors, which can affect how easily your blood clots.

Quick summary

["Assesses how your medications may alter your natural clotting process."]

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

Key facts at a glance

LOINC
7305-6
Short code
Endive IgG Qn
Synonyms
Endive IgG Qn
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
82784
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

This test evaluates the activity of vitamin K-dependent clotting factors in your blood, which are influenced by medications like warfarin (Coumadin®). It indirectly reflects how these medications are affecting your coagulation system by measuring the time it takes for blood to clot under controlled conditions.

Why It’s Ordered

Your healthcare provider may order this test if you’re on blood-thinning medications to monitor their effectiveness, check for bleeding risks, or adjust doses. It’s also used in patients with certain conditions like atrial fibrillation or those who’ve had heart valve replacements.

How the Test Works

Blood is drawn and analyzed to measure the prothrombin time (PT) or international normalized ratio (INR), which are indicators of how long it takes for blood to clot. This helps determine if your vitamin K-dependent clotting factors are functioning as expected with your medication.

What to Expect Before the Test

No special preparation is needed, but inform your provider about any medications, supplements, or recent illnesses that could affect results. Avoid aspirin or other blood thinners unless cleared by your doctor.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Vitamin K Antagonist Level

Frequently asked questions

How does this test help doctors manage my medication?
This test helps doctors monitor whether your blood-thinning medication is working properly. If your levels are too high, you may be at increased risk of bleeding. If they’re too low, your blood may clot too easily, increasing stroke or heart attack risk. Regular monitoring ensures your medication is adjusted safely.
What do abnormal results mean?
Higher-than-normal results may indicate your medication is too strong, requiring dose adjustments. Lower-than-normal results could mean your medication isn’t strong enough, increasing clot risks. Your provider will discuss these findings with you and adjust your treatment plan accordingly.
Can diet or supplements affect this test?
Yes, certain foods high in vitamin K (like leafy greens) or supplements containing vitamin K can interfere with results. Avoid large amounts of these for a few days before testing if instructed by your provider.
  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