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Protein C activity (serum/plasma)

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

This test measures how well your blood protein called Protein C works to help prevent blood clots.

Quick summary

["Protein C helps prevent dangerous blood clots; low levels may increase your risk of clotting problems."]

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

Key facts at a glance

LOINC
33407-8
Short code
Prot Pcar-mCnc
Synonyms
Prot Pcar-mCnc
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

What Is Protein C?

Protein C is a protein in your blood that plays a key role in preventing blood clots. When you have a clot, Protein C helps break it down and stop it from growing. Low levels of Protein C can make you more likely to develop clots, especially in veins or arteries.

Why Is This Test Done?

Your doctor may order this test if you have symptoms of blood clots (like swelling, pain, or redness in the legs), a history of clotting disorders, or if you’re taking blood thinners. It can also help diagnose or monitor conditions like antiphospholipid syndrome or inherited clotting disorders.

How Is the Test Performed?

A small blood sample is taken from a vein in your arm. The blood is then processed to measure Protein C activity using a specialized lab test that checks how effectively it works to prevent clotting.

What Do the Results Mean?

Results are usually reported as a percentage of normal activity. Very low levels (below normal) may indicate a clotting disorder, while very high levels (rarely seen) could suggest certain medical conditions or medications. Your doctor will interpret results in the context of your symptoms and medical history.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Protein C Activity

Frequently asked questions

What causes low Protein C levels?
Low Protein C levels can be caused by inherited genetic mutations, certain medications (like oral contraceptives or blood thinners), liver disease, or conditions like disseminated intravascular coagulation (DIC). If you have a family history of clotting disorders, this test may be part of screening.
How often should I get this test?
Your doctor will determine how often you need this test based on your medical needs. For example, if you have an inherited clotting disorder, you may need regular monitoring. If you’re taking blood thinners, your doctor may check Protein C levels occasionally to adjust your treatment.
Can I eat or drink before the test?
You can eat and drink normally before the test unless your doctor instructs otherwise. Avoiding food or fluids for a set period (like fasting) is not required for this test.
  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