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Platelet Factor 4 (PF4) / Heparin Complex (Antithrombin III) Antibody (Serum)

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

This test measures antibodies that may form a complex with Platelet Factor 4 (PF4) and antithrombin III, sometimes linked to certain blood clotting disorders or allergic reactions.

Quick summary

["Helps assess rare blood disorders or reactions to medications."]

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

Key facts at a glance

LOINC
56019-3
Short code
PA Bld Thromb ATP secr 1 U/mL
Synonyms
PA Bld Thromb ATP secr 1 U/mL
Category
hematology
Sample
whole-blood
Container
Lavender-top (EDTA)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
aggregometry-thrombin-induced-atp-secretion-u-ml
Specimen volume
3 mL
Stability
Room temperature: 4h, Refrigerated: 24h
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
4–24 hours
Order
routine

Why This Test Might Be Ordered

Your doctor may recommend this test if you have symptoms like unexplained bruising, bleeding, or allergic reactions after receiving certain medications (e.g., heparin). It may also be used to investigate suspected heparin-induced thrombocytopenia (HIT) or other autoimmune conditions affecting blood clotting.

What to Expect During the Test

A small needle will be used to draw blood from a vein in your arm. You may feel a slight pinch, but it usually takes only a few minutes. No special preparation is needed.

Common Causes or Triggers

This test is often triggered by exposure to heparin (a blood thinner), autoimmune conditions, or unexplained bleeding disorders. Rarely, it may be performed as part of a broader evaluation for unexplained clotting or allergic reactions.

What the Results Mean

Results are qualitative (positive or negative) and indicate the presence or absence of specific antibodies. Positive results may suggest an immune response affecting blood clotting, but further testing and clinical correlation are needed.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance: This test is primarily used to diagnose or rule out heparin-induced thrombocytopenia (HIT) or other rare autoimmune conditions involving PF4/ATIII antibodies. Positive findings may guide treatment adjustments, such as avoiding heparin or using alternative anticoagulants.

Short name

PF4/ATIII Antibody

Frequently asked questions

How often will I need this test?
The frequency depends on your symptoms, medical history, and treatment plan. Your doctor will determine how often you need follow-up testing, which may include repeat blood draws or additional evaluations.
What are the typical side effects of this test?
The most common side effect is mild bruising or soreness at the needle insertion site. Rarely, there may be a slight reaction at the injection site if heparin was recently administered.
Can I drink alcohol before this test?
No, avoid alcohol for 24 hours before the test, as it may affect blood test results. Follow your doctor’s specific instructions for any dietary or lifestyle restrictions.
  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