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Platelet Factor 4 (PF4) / Heparin Co-Factor III (HCIII) Antithrombin Complex (Serum)

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

This test measures the interaction between Platelet Factor 4 (PF4) and Antithrombin III (HCIII) in your blood, which helps assess how well your blood can naturally prevent clots from forming.

Quick summary

["This test helps evaluate your body’s natural anticoagulant system and may be used in monitoring or diagnosing bleeding disorders or clotting risks."]

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

Key facts at a glance

LOINC
96685-3
Short code
Clt Frm+PltFn Gls -Hep Pnl Bld MicrVisc
Synonyms
Clt Frm+PltFn Gls -Hep Pnl Bld MicrVisc
Category
hematology
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
microviscometry
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

Platelet Factor 4 (PF4) is a protein released by platelets that binds to heparin and Antithrombin III (HCIII) to inhibit clotting. This complex helps identify if your blood has enough natural anticoagulant activity, which is important for preventing abnormal clotting.

Why It’s Done

Your healthcare provider may order this test if you have symptoms of bleeding disorders, such as easy bruising or prolonged bleeding, or if you’re taking anticoagulant medications. It can also help monitor conditions like heparin-induced thrombocytopenia (HIT) or evaluate bleeding risks in certain surgeries.

How It’s Performed

A blood sample is drawn from a vein, typically in your arm. The serum (liquid part of blood after clotting) is then analyzed to measure the PF4/HCIII complex levels.

What the Results Mean

Lower than expected levels of this complex may suggest insufficient anticoagulant activity, which could indicate bleeding risks or other underlying clotting disorders. Higher-than-expected levels might be seen in certain clotting conditions or during specific medical treatments.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

PF4/HCIII Complex

Frequently asked questions

What does a low PF4/HCIII complex mean?
A low result may indicate an issue with your blood’s ability to naturally prevent clots, which could be due to a deficiency in Antithrombin III or other clotting factors. This may require further evaluation by your healthcare provider to determine the best course of action.
How often should I get this test?
The frequency depends on your medical condition, treatment plan, and symptoms. Your healthcare provider will decide how often you need this test based on your individual needs, such as monitoring for bleeding risks or response to medications.
Can diet or lifestyle affect this test?
Diet or lifestyle factors typically do not directly affect PF4/HCIII complex levels. However, if you’re on medications like heparin or warfarin, your provider may adjust your treatment based on these test results.
  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