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Protein C Activity (Serum)

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

This test measures the activity level of Protein C, a natural blood protein that helps prevent blood clots from forming inappropriately. It plays a key role in maintaining healthy blood flow and is often checked in patients with a history of blood clots or clotting disorders.

Quick summary

["Protein C helps regulate blood clotting; low levels may increase clot risk."]

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

Key facts at a glance

LOINC
80226-4
Short code
Type of Pig cath
Synonyms
Type of Pig cath
Category
chemistry
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 Might Be Ordered

Your doctor may order this test if you have symptoms of blood clots (such as swelling, pain, or redness in the legs or arms), a history of clotting disorders, or if you’re taking blood thinners. It may also be part of a broader evaluation for conditions like antiphospholipid syndrome or inherited clotting disorders.

What to Expect Before the Test

No special preparation is needed, but you may be asked to fast for 8–12 hours before the draw if your lab uses a specific method. Bring any medications or supplements you’re taking, as they could affect results.

What Happens During the Test

A healthcare provider will draw blood from a vein in your arm. You may feel a slight pinch, but the procedure is quick. The blood sample is sent to a lab for testing Protein C activity levels.

What the Results Mean

Results are reported as a percentage of normal activity (e.g., 50% means half the normal level). Low levels may indicate a higher risk of clots, while normal or high levels suggest no immediate concern. Your doctor will interpret results in the context of your medical history.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Protein C Level

Frequently asked questions

What does a low Protein C level mean?
A low Protein C level may increase your risk of blood clots, especially if you have other risk factors like pregnancy, surgery, or certain medications. It can also be linked to inherited clotting disorders or conditions like liver disease, which affect protein production.
What does a high Protein C level mean?
High Protein C levels are less common and usually not directly harmful unless they occur alongside other clotting risks. In some cases, they may be associated with conditions like cancer or certain medications, but further evaluation is needed to determine the cause.
How often should I get this test?
Your doctor will decide how often you need this test based on your medical needs. If you have a clotting disorder, it may be part of routine monitoring. If you’re healthy, it’s unlikely to be repeated unless symptoms or risk factors change.
  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