Protein C Blood Test – Indications, Procedures, Results

Last updated: February 8, 2026 Medically reviewed by: RxHarun Orthopedic Specialist Doctor Reading time: 2 min read

Protein C is a normal substance in the body that prevents blood clotting. A blood test can be done to see how much of this protein you have in your blood.

How the Test is Performed

A blood sample is needed.

How to Prepare for the Test

Certain medicines can change blood test results.

Tell your health care provider about all the medicines you take.
Your provider will tell you if you need to stop taking any medicines before you have this test. This may include drugs that prevent blood clots (blood thinners).
Do not stop or change your medicines without talking to your doctor first.

How the Test will Feel

When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or slight bruising. This soon goes away.

Why the Test is Performed

You may need this test if you have an unexplained blood clot, or a family history of blood clots. Protein C helps control blood clotting. A lack of this protein or problem with the function of this protein may cause blood clots to form in veins.

The test is also used to screen relatives of persons who are known to have protein C deficiency . It may also be done to find the reason for repeated miscarriages.

Normal Results

Normal values are 60 to 150% inhibition.

Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or may test different samples. Talk to your doctor about the meaning of your specific test results.

What Abnormal Results Mean

A lack (deficiency) of protein C can lead to excess clotting . These clots tend to form in veins, not arteries.

Protein C deficiency can be passed down through families (inherited). It can also develop with other conditions, such as:

Chemotherapy use
Disorder in which the proteins that control blood clotting become over active ( disseminated intravascular coagulation )
Liver disease
Long-term antibiotic use
Warfarin (Coumadin) use

A problem such as a sudden blood clot in the lung may reduce the protein S level.

Protein C level rises with age, but this does not cause any health problems.

Risks

There is very little risk involved with having your blood taken. Veins and arteries vary in size so it may be harder to take a blood sample from one person than another.

Other slight risks from having blood drawn may include:

Excessive bleeding
Fainting or feeling lightheaded
Hematoma (blood accumulating under the skin)
Infection (a slight risk any time the skin is broken)

Frequently Asked Questions

Is this article a replacement for a doctor?

No. It is educational content only. Patients should consult a qualified clinician for diagnosis and treatment.

When should I seek urgent care?

Seek urgent care for severe symptoms, rapidly worsening condition, breathing difficulty, severe pain, neurological changes, or any emergency warning sign.

References

Add references, clinical guidelines, textbooks, journal articles, or trusted medical sources here. You can edit this area later with a custom field named _rx_references.

Written by Dr. Harun Ar Rashid, MD - Arthritis, Bones, Joints Pain, Trauma, and Internal Medicine Specialist

Dr. Md. Harun Ar Rashid, MPH, MD, PhD, is a highly respected medical specialist celebrated for his exceptional clinical expertise and unwavering commitment to patient care. With advanced qualifications including MPH, MD, and PhD, he integrates cutting-edge research with a compassionate approach to medicine, ensuring that every patient receives personalized and effective treatment. His extensive training and hands-on experience enable him to diagnose complex conditions accurately and develop innovative treatment strategies tailored to individual needs. In addition to his clinical practice, Dr. Harun Ar Rashid is dedicated to medical education and research, writing and inventory creative thinking, innovative idea, critical care managementing make in his community to outreach, often participating in initiatives that promote health awareness and advance medical knowledge. His career is a testament to the high standards represented by his credentials, and he continues to contribute significantly to his field, driving improvements in both patient outcomes and healthcare practices. Born and educated in Bangladesh, Dr. Rashid earned his BPT from the University of Dhaka before pursuing postgraduate training internationally. He completed his MD in Internal Medicine at King’s College London, where he developed a special interest in inflammatory arthritis and metabolic bone disease. He then undertook a PhD in Orthopedic Science at the University of Oxford, conducting pioneering research on cytokine signaling pathways in rheumatoid arthritis. Following his doctoral studies, Dr. Rashid returned to clinical work with a fellowship in interventional pain management at the Rx University School of Medicine, refining his skills in image-guided joint injections and minimally invasive pain-relief techniques.